WO2004001808A2 - Method and system for atomic layer removal and atomic layer exchange - Google Patents

Method and system for atomic layer removal and atomic layer exchange Download PDF

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Publication number
WO2004001808A2
WO2004001808A2 PCT/US2003/019982 US0319982W WO2004001808A2 WO 2004001808 A2 WO2004001808 A2 WO 2004001808A2 US 0319982 W US0319982 W US 0319982W WO 2004001808 A2 WO2004001808 A2 WO 2004001808A2
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Prior art keywords
gas
reaction
solid compound
reactive gas
layer
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PCT/US2003/019982
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French (fr)
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WO2004001808A8 (en
WO2004001808A3 (en
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Kerem Kapkin
Sang-In Lee
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Aviza Technology, Inc.
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Priority to AU2003245677A priority Critical patent/AU2003245677A1/en
Publication of WO2004001808A2 publication Critical patent/WO2004001808A2/en
Publication of WO2004001808A3 publication Critical patent/WO2004001808A3/en
Publication of WO2004001808A8 publication Critical patent/WO2004001808A8/en

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    • H—ELECTRICITY
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/28008—Making conductor-insulator-semiconductor electrodes
    • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
    • H01L21/28158—Making the insulator
    • H01L21/28167—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation
    • H01L21/28185—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation with a treatment, e.g. annealing, after the formation of the gate insulator and before the formation of the definitive gate conductor
    • 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]
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    • H01L21/0206—Cleaning during device manufacture during, before or after processing of insulating layers
    • H01L21/02063—Cleaning during device manufacture during, before or after processing of insulating layers the processing being the formation of vias or contact holes
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
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    • H01L21/28194—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation by deposition, e.g. evaporation, ALD, CVD, sputtering, laser deposition
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
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    • H01L21/28211—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation in a gaseous ambient using an oxygen or a water vapour, e.g. RTO, possibly through a layer
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3105—After-treatment
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3105—After-treatment
    • H01L21/311—Etching the insulating layers by chemical or physical means
    • H01L21/31105—Etching inorganic layers
    • H01L21/31111—Etching inorganic layers by chemical means
    • H01L21/31116—Etching inorganic layers by chemical means by dry-etching
    • H01L21/31122—Etching inorganic layers by chemical means by dry-etching of layers not containing Si, e.g. PZT, Al2O3
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
    • H01L21/32133—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only
    • H01L21/32135—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only
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    • 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
    • H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
    • H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
    • H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
    • H01L21/76814—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics post-treatment or after-treatment, e.g. cleaning or removal of oxides on underlying conductors
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    • H01L29/517—Insulating materials associated therewith the insulating material comprising a metallic compound, e.g. metal oxide, metal silicate
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    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
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    • H01L29/518—Insulating materials associated therewith the insulating material containing nitrogen, e.g. nitride, oxynitride, nitrogen-doped material

Definitions

  • the present invention relates generally to the field of semiconductors. More specifically, the present invention relates to atomic layer removal and atomic layer exchange of films on semiconductor devices and wafers.
  • MOS metal oxide silicon
  • prior art deposition techniques such as chemical vapor deposition (CND) are increasingly unable to meet the requirements of advanced thin films. While CND processes can be tailored to provide conformal films with improved step coverage, CND processes often require high processing temperatures, result in incorporation of high impurity concentrations, and have poor precursor or reactant utilization efficiency.
  • one of the obstacles of making high-k gate dielectrics is the formation of an interfacial silicon oxide layer during CND processing.
  • Another obstacle is the limitation of prior art CND processes in depositing ultra thin films for high-k gate dielectrics on a silicon substrate.
  • Techniques well known in the art are used to remove or etch films used in semiconductor device manufacturing. These techniques include wet etching, plasma etching, and the like. The mechanism of these techniques do not allow control of material removal on the atomic scale. It is common that different materials have different rates of etching under the same conditions.
  • Figures 1 and 2 illustrate problems with prior art methods for treating a multilayer stack of substrate layers.
  • a stack comprising SiO 2 , Si 3 ⁇ 4 , and Al 2 O 3 layers on a substrate is treated with a hydrofluoric acid (HF) bath. Because the HF etches different materials at different rates, the resultant stack has an undesirable jagged edge.
  • an HF etch is used to remove the oxide layer at the bottom of a contact hole through a film stack containing layers of high temperature oxide (HTO), Si 3 N , SiO 2 , high temperature oxide (HTO), and boro- phosphate silicate glass (BPSG) atop a silicon substrate.
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • HTO high temperature oxide
  • BPSG boro- phosphat
  • the resultant contact hole has a "jagged edge" wall structure.
  • This uneven structure presents substantial difficulties when the contact hole is coated with a barrier layer, for example of tantalum nitride (TaN).
  • the barrier layer of TaN is added to prevent metal ions, such as for example copper, from diffusing into the dielectric (SiO 2 ) layers of the wafer.
  • Metal atoms are a substantial source of leakage current.
  • surface nonconformities tend to create discontinuities in the coating. These discontinuities may provide leakage paths for metal to enter the coated layers as shown in Figure 3.
  • the effects of non-uniform contact hole side walls is magnified as device dimensions shrink.
  • the present invention provides a method and system for modifying the surface of a substrate such as a semiconductor device or wafer by atomic layer removal (ALR) and/or atomic layer exchange (ALEx).
  • ARR atomic layer removal
  • ALEx atomic layer exchange
  • Advantages of the present invention may be realized by the ALR and ALEx method and system described herein in which a method is provided for uniformly removing a layer of molecules of a first solid compound from a surface of a substrate.
  • the substrate is exposed to a first reactive gas that reacts with a first layer of molecules on the surface to form a mono-layer of molecules of an intermediate solid compound on the surface.
  • a second reactive gas is introduced.
  • the second reactive gas reacts with the intermediate solid compound to form a volatile or volatihzable product.
  • the second reactive gas and the volatile or volatihzable product are then removed from contact with the substrate which has one fewer molecular layers of the first solid compound on its surface.
  • a method of atomic layer exchange is provided.
  • a film having multiple atomic layers formed on a substrate, and comprising at least one molecular layer of a first solid compound having at least a first and a second solid chemical species is exposed to a first reactive gas.
  • the first reactive gas has at least a first and a second gas chemical species.
  • a surface reaction occurs wherein the first solid chemical species is exchanged with the first gas chemical species to form an intermediate solid compound.
  • the substrate is a second reactive gas which reacts with the intermediate solid compound to produce one or more volatile products, leaving the film of the first solid compound with one fewer molecular layers than it started with.
  • Figure 1 is a schematic diagram showing the effects of a prior art hydrofluoric acid bath etch treatment on a stack of different chemical layers.
  • Figure 2 is a schematic diagram showing the effects of a prior art hydrofluoric acid bath etch treatment on the walls of a contact hole through layers of different solid materials.
  • Figure 3 is a schematic diagram illustrating the effects of uneven contact hole walls resulting from prior art etch techniques on TaN barrier layer coating and the resultant diffusion of metal ions into SiO 2 and Si 3 N layers on a semiconductor wafer.
  • Figure 4 is a schematic view illustrating the steps of the atomic layer removal method according to one embodiment of the present invention.
  • Figures 5 A to 5D are schematic illustrations of the steps of an atomic layer removal method according to another embodiment of the present invention.
  • Figures 6A to 61 are schematic diagrams illustrating the steps of atomic layer exchange followed by atomic layer removal according to another embodiment of the present invention.
  • Figure 7 is a schematic diagram showing illustrating the improvement in side- wall uniformity relative to prior art methods resulting from treatment of a semiconductor wafer contact hole through layers of different solid materials using a method according to the present invention
  • Figure 8 is a schematic diagram illustrating the steps of an atomic layer removal technology according to the present invention, in which the silicon substrate is passivated to HF attack by creation of a H-terminated, hydrophobic surface prior to exposure to HF vapor, to uniformly remove a surface mono-layer of molecules from each of the layers in a wafer stack.
  • Figure 9 is a flow chart outlining the steps of an atomic layer removal method according to one embodiment of the present invention.
  • the present invention provides an atomic layer removal and atomic layer exchange method and system.
  • ARR abbreviation
  • atomic layer exchange atomic layer exchange
  • the two processes are related as each method may be used to remove the surface layer of a solid compound from a substrate.
  • ALEx can also be used to modify the surface of the
  • the present invention provides an atomic layer removal and atomic layer exchange method and system where a substrate having a film deposited or grown on the surface of the substrate is placed in a reactor or chamber.
  • a first reactant gas is introduced into the reactor or chamber to react with a first layer of the film to convert the first layer into a mono-layer of a solid compound.
  • the reactor or chamber is purged to remove unreacted first reactant gas and/or any gas-phase products.
  • a second reactant gas is then introduced into the reactor or chamber to react with the mono-layer of the solid compound to form a gaseous compound, which is removed from the reactor by a second purging step.
  • the first reactant gas may require the addition of a source of energy to activate or facilitate the reaction of the first reactant gas with the first layer of the film.
  • the energy source may be in the form of electromagnetic radiation or some other energy delivery method. Examples of this electromagnetic radiation include, but are not limited to, visible light radiation, infrared radiation, ultraviolet radiation, microwave radiation, radio frequency radiation, and the like.
  • the radiation may be supplied in a coherent form from a device such as a laser, or in a non-coherent (i.e. out of phase) form from a device such as a lamp.
  • the use of the energy source will facilitate the reaction of the first reactant gas with the first layer of the film.
  • the present invention may be utilized for the removal of single atomic layers from the surface of the wafer.
  • the atomic layer removal process is a self terminating sequential atomic layer removal process. This process may be used to remove a wide variety of compounds from a surface prior to a subsequent deposition process.
  • the removed compounds may comprise intentionally or incidentally deposited oxide coatings as well as solid substrate material and/or compounds deposited in layers by chemical vapor deposition, among others.
  • the present invention may be used to reduce a deposited conductive or dielectric film thickness to achieve a desired final film thickness. These are just a few of the applications of the present invention.
  • a first reactive gas is reacted with the top layer of a film to convert the top layer to a mono-layer of a solid compound.
  • the first reactive gas is a chemical agent that converts an atomic layer of a fist solid compound in the surface film or upper layer of a substrate to a mono-layer of an intermediate solid compound which can be further reacted with a second reactive gas.
  • the selection of the first reactive gas depends on the molecular composition of the film and the chemistry of the first solid compound.
  • the mono-layer of the intermediate solid compound is then reacted with a second reactive gas to form a volatile or volatihzable product.
  • a substrate 10 having a film 12 deposited or grown on the surface of the substrate is placed in a reactor, chamber, or some other environment in which its exposure to a sequence of reactive gases may be controlled.
  • the film is typically comprised of multiple atomic layers, in this example, of a first solid compound A( S0 Hd).
  • the film of A (S0Hd) is 3 molecular layers thick.
  • any thickness of film and/or other solid or deposited surface compound may be treated according to the present invention.
  • the number of molecular or atomic layers of the first solid compound present on the surface of the substrate may vary widely depending on the specific application.
  • the first solid compound, A (SO ii d to be removed may include any type of film used in semiconductor processing such as any gate dielectric or ceramic, to metal oxides, silicon oxides, metal aluminates, silicon aluminates, metal silicates, metal nitrides, silicon nitrides, pure metals or other films commonly found in semiconductor devices.
  • any surface may be treated using the method of the present invention provided the proper reactive gases are chosen.
  • the substrate 10 and film 12 shown in panel (I) are exposed to a first reactive gas B( gas ).
  • the B( gas ) is preferably a chemical agent that converts an atomic and/or molecular layer of the first solid compound A (SO ii d) on the film or substrate surface to a mono-layer of an intermediate solid compound D( S0 ii d) .
  • the first reactant gas B ( g as) is selected to react with the first solid compound A (sol j d) to form a mono- layer of the intermediate solid compound D (S0Ud) on the substrate surface.
  • the reaction of the first reactive compound B (gas ) with the first solid compound A( SO ud) is preferably either thermodynamically favored and/or kinetically favored relative to the reaction of the mono-layer of the intermediate solid compound D (SO ii d) - hi other words, the reaction of the first reactive compound B( gas ) with the clean A (SO ii d) surface should result in formation of a uniform surface coated with a mono-layer of the intermediate solid compound D (so ⁇ id) .
  • Thermodynamically favored, as used above, means that the reaction of B( gas ) with D (SO n d) according to
  • reaction B(gas) + D(solid) - (3) is substantially less exothermic than reaction (1). Kinetically favored as used above indicates that reaction (3) proceeds at a substantially slower reaction rate than reaction (1). It is also preferable that the intermediate solid compound D (SO ⁇ d) forms a layer that retards contact between additional gas-phase molecules of the first reactive gas B ( g as) with underlying layers of the first solid compound A (SO ii d) so that only a mono- layer of D (So ii d) is formed.
  • Examples of compounds for use as the first reactant gas B (gas) according to the present invention include but are not limited to: ozone, hydrogen, alcohols, water, ammonia, and the like.
  • first reactive gas B converts the surface layer 14 of first solid compound A (so ij ) molecules to a mono-layer of intermediate solid compound D (so n ) .
  • first reactant gas B gas
  • the substrate is then exposed to a second reactive gas, C (gaS) , which converts the surface mono-layer of intermediate solid compound D (sol j d) to a volatile or volatihzable product E (gas) as shown in panel (III).
  • the second reactive gas C (gas) is preferably chosen such that its reaction with the mono-layer of intermediate solid compound D( so ii d) is either substantially more exothermic (thermodynamically favored) or proceeds at a substantially faster reaction rate (kinetically favored) than the reaction of C (gas ) with the film compound A( S0 iid). hi other words, it is preferred that
  • the second reactive gas C (g as ) that reacts with the converted mono-layer of the intermediate solid compound D(soiid) may be a halogen containing source.
  • halogen containing compounds applicable to this method include, but are not limited to C1F , NF , HF and chlorine.
  • the volatile or volatihzable product E (gas) volatilizes or is volatilized from the surface to leave film 12 which, in the present example shown in Figure 4, then contains two molecular layers of solid compound A (S0Hd) , one layer less than prior to treatment.
  • first and second reactive gases are each introduced into the reactor or chamber for a period of time sufficient to react with one mono, or atomic/molecular, layer on the film. Exposure times for the first and second reactive gases are generally on the order of approximately one half to sixty seconds, or more specifically in the range of approximately one to two seconds.
  • the film or wafer surface is comprised of a first and a second solid compound, A and B respectively, as shown in Figure 5A.
  • the wafer surface may contain a film, or may contain only silicon with a native oxide formed thereon.
  • atomic layer exchange takes place, and the wafer is exposed to a gaseous precursor CD as shown in Fig. 5B.
  • a surface reaction and exchange of species occurs with the top layer on the wafer.
  • the surface reaction converts the top layer to a mono-layer of solid compound AD( SO iid).
  • a "waste" gaseous compound of CB (gas ) is also formed which is removed or purged from the chamber as previously described and shown in Figure 5D.
  • the steps may be summarized by the following equation: AB (solid ) + CD (gas ) -» AD (so ii d) + CB(gas) (5)
  • gaseous precursors or reactants may be employed with the method of the present invention, and will be selected based in part on the chemical composition of the film. Additional examples of gaseous precursors include, but are not limited to ozone, ammonia, water, hydrogen, hydrazine, alcohols, halogens, and the like. As described above, atomic layer exchange takes place between free radicals or molecules in the gas phase and the wafer or film or substrate surface. Diffusion of these gaseous precursors through the wafer surface may be controlled by a number of parameters, including temperature, pulse time, chamber pressure, molecule size and reactivity - to avoid multi-layer atomic exchange.
  • FIG. 6A to 61 Another embodiment of the method of the present invention is illustrated more specifically in Figures 6A to 61, which show sequential steps in detail, h this example, atomic layer exchange and atomic layer removal are carried out.
  • atomic layer exchange is carried out to modify the chemistry of the film surface according to the following equation: CB (solid) + DE (gas) ⁇ CE (so ii d) + DB(gas) T (6) where CB (SO ⁇ d) is The first reactive gas DE( gaS) is conveyed to the reactor or chamber as shown in Figure 6B.
  • the first reactive gas DE (gas) is optionally activated to form one or more first gas-phase radical species as shown in Figure 6C.
  • activation may take place by a variety of means, such as by temperature, energy pulse, electromagnetic radiation, and the like.
  • first reactive gas DE gas
  • activation is not necessary for the reaction to proceed.
  • Atomic layer exchange with the top layer of the film takes place.
  • the resultant surface layer of the film is then an intermediate solid compound CE( so iid) as shown in Figure 5D.
  • the chamber or reactor is purged and the formed first gaseous by-product DB (gaS) as well as any unreacted first reactive gas
  • a second reactive gas XY gas
  • the second reactive gas XY may optionally be activated to form one or more second gas-phase radical species, such as by energy pulse, temperature, or electromagnetic radiation or other means as shown in Figure 6G.
  • reaction products in the gas phase are:
  • native oxide contamination at the bottom of a contact hole formed by reactive ion etch or some comparable method in a multi-layer stack of deposited substrate material may be removed via exposure of the substrate and multi-layer stack to a solution of hydrofluoric acid (HF bath).
  • HF bath hydrofluoric acid
  • the removal of material from the exposed layer surfaces in a reactive etch bath is reaction rate limited, and the etchant reacts with different layer materials at different rates, so the traditional wet etch technique results in a non-planar sidewall after the etch.
  • the oxide layer at the bottom of a contact hole formed through a multi-layer stack of material is removed without formation of a non-planar hole.
  • the present invention is used to remove the oxide at the bottom of the contact hole while maintaining the planarity of the sidewall. Because the method of the present invention uniformly removes a single mono-layer regardless of the reactivity of the surface compound in each reaction cycle, the process avoids the problems of kinetic-driven wet etching in which more reactive materials are etched away at faster rates than less reactive materials.
  • water is used as the first reactant gas to form an — OH terminated surface on all of the exposed oxide surfaces. Dielectric films of silicon oxides and metal oxides are hydrophilic and this reaction proceeds easily.
  • HF is then introduced as the second reactant gas and removes the top layer of the film in the form of water and SiF 4 or metal fluoride.
  • the reaction of HF with silicon oxides or metal oxides in the absence of water is very slow. Therefore, the reaction will self-terminate when the first layer is removed. This sequence can be repeated until the oxide at the bottom of the contact hole is removed. Since each cycle removes only one layer, regardless of the chemical nature of the oxide, the planarity of the sidewall will be retained.
  • the steps according to one embodiment of the present invention as shown in Figure 8 are (I) passivation of the non-oxide surfaces by exposure to hydrogen gas with UV activation, (II) introduction of water vapor (first reactive gas) or some other source, such as an alcohol, of hydroxyl ions and/or hydroxyl radicals, to change and standardize the surface state of the dielectric/oxide layers, (III) optional purging of the chamber/reactor to remove the water vapor, (TV) introduction of HF vapor to remove a surface layer of molecules for the dielectrics and oxides, and (V) repeat of steps (II)- (V) to remove additional layers as needed.
  • first reactive gas water vapor
  • some other source such as an alcohol, of hydroxyl ions and/or hydroxyl radicals
  • this technique is advantageous relative to the prior art HF etch method in which the substrate and dielectric layers are dipped in an aqueous bath of HF.
  • the resulting non-uniform surface of contact holes and other surfaces featuring a number of different dielectric or oxide layers is avoided by the method of the present invention because the reaction of HF vapor with a hydroxylized surface proceeds only to remove the hydroxyl group (as water vapor) and its associated atom, as for instance SiF 4 or A1F 3 for SiO and Al O 3 , respectively.
  • the oxide-HF reaction occurs once, the remaining non- hydroxylized surface is substantially less reactive to HF attack than the surface with attached hydroxyl groups.
  • FIG. 9 summarizes the steps of a method of ALR and/or ALEx according to the present invention.
  • a substrate containing one or more films and/or solid compound layers is placed in a reactor, chamber, or other system for providing a controlled atmosphere to the surface in step 300.
  • Any hydrophobic surfaces on the substrate may optionally be passivated by, for example exposing the substrate to hydrogen gas or some other compound that will react with surface oxide deposits to provide a surface that will not adsorb water vapor in step 302.
  • This passivation step 302 may be activated by irradiating the gas mixture in the reactive atmosphere above the substrate with ultraviolet light sufficient to break molecular bonds in gas phase hydrogen or whatever passivating gas is used.
  • the passivation step 302 also includes purging of the reactor or chamber to remove the passivating gas.
  • a first reactive gas is introduced to the atmosphere above the substrate in step 304.
  • the first reactive gas may be a source of oxygen such as for instance ozone, water, or an alcohol.
  • the first reactive compound may be hydrogen or ammonia or some similar compound.
  • the exact choice of a compound for use as the first reactive gas is made based on the desired intermediate reaction product and its reactivity with the chosen second reactive gas as discussed below. A knowledge of gas- and surface-phase chemistry characteristic of one of skill in the art and routine experimentation are sufficient to determine the proper combination of first and second reactive gases based on the substrate to be treated.
  • the first reactive compound may optionally be activated via electromagnetic radiation such as is discussed above or by some other energy input such as radiative, conductive, or convective heating in step 306.
  • some reactive gases may "self-activate" or react spontaneously with the film surface or interest.
  • the reaction is activated or not, the first reactive gas reacts with the surface mono-layer of the substrate surface to form a molecular layer of an intennediate solid compound in step 310.
  • the first reactive gas is preferably chosen such that the reaction of the first reactive gas with the substrate or film surface proceeds to effective completion with the conversion of one surface layer of molecules from the starting solid compound to the intermediate solid compound.
  • the first reactive gas does not further react with the intermediate solid compound, nor does the first reactive gas diffuse through the surface mono-layer of the intermediate solid compound to react with additional layers of the starting solid compound below the gas-solid surface.
  • these limitation can be either thermodynamic or kinetic.
  • the reaction of the first reactive gas with the intermediate solid compound is substantially less thermodynamically favored relative to the reaction of the first reactive gas with the starting solid compound.
  • the rate of the reaction of the first reactive gas with the starting solid compound proceeds at a much faster rate than either the reaction of the first reactive gas with the intermediate solid compound or the reaction of the first reactive gas with layers of the starting solid compound that underlie the surface mono-layer of the intermediate solid compound.
  • the chamber or reactor is purged to clear any remaining gas from contact with the substrate in step 312.
  • the length of exposure of the substrate to the first reactive gas depends on the kinetics and thermodynamics of the reaction, but is generally in the range of one to 60 seconds. Shorter reaction times of approximately half a second to one second may be used for very reactive gases. In general, however, the exposure time for the first reactive gas is in the range of approximately one to two seconds.
  • a second reactive gas is then introduced to the chamber or reactor in step 314.
  • the second reactive gas is chosen such that its reaction with the intermediate solid compound formed in step 310 proceeds to effective completion by converting the intermediate solid compound to a higher vapor pressure compound or compounds that either volatilize from the substrate surface or are readily volatilized via some energy input such as heating.
  • the second reactive gas is a halogen- containing oxidizer compound. Suitable compounds include, but are not limited to C1F , NF 3 , HF, and chlorine gas. However, one of ordinary skill in the art may to select other compounds that are commensurate with the scope of the present invention based on the teachings provided herein.
  • the second reactive gas may optionally be activated by some energy input such as has been described above in step 316.
  • activation may or may not be necessary.
  • the second reactive gas is exposed to the substrate for a reaction time in the range of approximately 0.5 to 60 seconds, with typical reaction times in the range of approximately one to two seconds.
  • the second reactive gas reacts with the intermediate solid compound to convert the intermediate solid compound to a volatile or volatihzable product that either enters the gas phase immediately upon its formation or is readily evaporated from the surface in step 320.
  • the second reactive gas is preferably selected to react substantially only with the compound of the intermediate solid compound formed as a mono-layer in step 310.
  • the limitation on the reaction of the second reactive gas with the starting solid compound maybe either kinetic or thermodynamic as described above in regards to the first reactive compound.
  • the reaction of the second reactive gas with the starting solid compound is substantially less thermodynamically favored than that of the second reactive gas with the intermediate solid compound.
  • the rate at which the reaction of the second reactive gas with the intermediate solid compound proceeds is substantially faster than the rate at which the reaction of the second reactive gas with the starting solid compound proceeds. If the volatile or volatihzable product does not substantially evaporate from the substrate surface upon formation, energy or some other evaporative inducement is provided via radiation, heat, or some other known technique to cause the volatile or volatihzable product to be released to the gas phase in step 322.
  • steps 304-324 may be repeated multiple times.
  • the optional passivation step is only used at the start of the process. Subsequent layers may be removed without re-passivating.
  • the method of the present invention can be used to deposit an ultra thin film on a substrate with tightly controlled dimensions.
  • prior art deposition technology has limitations in depositing a dielectric film having an ultra-thin thickness, such as a thickness of 3 A.
  • a dielectric film having a thickness of, e.g. 10 A can be first deposited on the surface of a substrate. Then layers of the dielectric films can be removed from the substrate using the atomic layer removal method as described above. There is no limitation on the number of layers to be removed.
  • layers of a thickness of 7 A of the dielectric film can be removed by repeating the steps as described above, leaving a film with a thickness of 3 A remaining on the surface of the substrate.
  • the atomic layer removal and atomic layer exchange method of the present invention has broad applications.
  • the present invention can be used to etch metals and dielectrics, generate photolithographic masks, and improve resolution of liquid crystal displays, among other applications.
  • atomic layer removal of the present invention may be used for reducing final film thicknesses and/or removing undesired surface roughness prior to forming gate electrodes.
  • the silicon - high K dielectric interface may be controlled by atomic layer exchange of the present invention along with low temperature ALD high K dielectric processes.
  • a layer of titanium nitride is provided, and the removal to a desired thickness is achieved by the method and system of the present invention.
  • Titanium nitride (TiN) is a preferable material for gate electrode barrier.
  • a relatively thick TiN film can be pre-deposited on the surface of a gate dielectric.
  • ozone gas is introduced to convert the top atomic layer of TiN film to a mono-layer of titanium dioxide (TiO 2 ).
  • the solid TiO layer is then further reacted with hydrogen fluoride (HF) vapor to form gaseous titanium fluoride (TiF 4 ) and water, which are removed from the reactor.
  • HF hydrogen fluoride
  • Each cycle of the method can remove one atomic layer of TiN from the substrate.
  • an ultra thin TiN film of a desired thickness can be achieved on a silicon substrate.
  • Example 2 hi another example, ethanol is used as a first reactant gas to react with silicon dioxide (SiO 2 ) film pre-deposited on a substrate. A mono-layer of silicon hydroxide (SiOH) is formed on the top surface of the substrate.
  • Hydrogen fluoride (HF) is used as a second reactant gas to react with the solid silicon hydroxide to form gaseous silicon fluoride (SiF 4 ) and water, which are removed from the reactor.

Abstract

A method and system for atomic layer deposition and removal of a dielectric film are provided. The present invention comprises introducing a first reactant gas into a reactor to react with a first layer of the film to convert the first layer into a mono?layer of a solid compound; introducing a second reactant gas into the reactor to react with the mono?layer of the solid compound to form a gaseous compound; and removing the gaseous compound. Preferably, the mono?layer of the solid compound needs less energy to react with the second reactant gas than a next layer of the film underneath the mono?layer of the solid compound. In another aspect of the present invention a gas reactant having two or more chemical species is exposed to the film and a surface reaction occurs wherein certain of the chemical species in the gas reactant are exchanged with certain chemical species in the top atomic layer of the film.

Description

METHOD AND SYSTEM FOR ATOMIC LAYER REMOVAL AND ATOMIC LAYER EXCHANGE
RELATED APPLICATIONS
This application claims the benefit of United States Provisional Application Serial Number 60/391,011, filed on June 23, 2002, the disclosure of which is hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates generally to the field of semiconductors. More specifically, the present invention relates to atomic layer removal and atomic layer exchange of films on semiconductor devices and wafers.
BACKGROUND OF THE INVENTION
Next generation semiconductor devices require thin dielectric films for metal oxide silicon (MOS) transistor gates, and capacitor dielectrics. As oxides are scaled down, the tunneling leakage current becomes significant and limits the useful range for gate oxides to about 1.8 nm or more.
High dielectric constant metal oxides such as hafnium oxide (HfO2, k=20), zirconium oxide (ZrO2, k=20), and Hf and Zr silicates are considered alternative materials to silicon oxide (k=3.9) to provide gate dielectrics with high capacitance without compromising the leakage current. However, prior art deposition techniques such as chemical vapor deposition (CND) are increasingly unable to meet the requirements of advanced thin films. While CND processes can be tailored to provide conformal films with improved step coverage, CND processes often require high processing temperatures, result in incorporation of high impurity concentrations, and have poor precursor or reactant utilization efficiency. For instance, one of the obstacles of making high-k gate dielectrics is the formation of an interfacial silicon oxide layer during CND processing. Another obstacle is the limitation of prior art CND processes in depositing ultra thin films for high-k gate dielectrics on a silicon substrate. Techniques well known in the art are used to remove or etch films used in semiconductor device manufacturing. These techniques include wet etching, plasma etching, and the like. The mechanism of these techniques do not allow control of material removal on the atomic scale. It is common that different materials have different rates of etching under the same conditions. Therefore, when a typical etching technique is applied to a feature such as a hole, channel, or via through a multi-layer stack of different materials, the sidewall of the feature cannot be maintained in a straight and uniform manner. This causes difficulties for the deposition of subsequent materials into the feature in a continuous manner. Therefore, these techniques cannot be used to accurately remove films one atomic layer at a time.
Figures 1 and 2 illustrate problems with prior art methods for treating a multilayer stack of substrate layers. In Figure 1, a stack comprising SiO2, Si3Ν4, and Al2O3 layers on a substrate is treated with a hydrofluoric acid (HF) bath. Because the HF etches different materials at different rates, the resultant stack has an undesirable jagged edge. Likewise, in Figure 2, an HF etch is used to remove the oxide layer at the bottom of a contact hole through a film stack containing layers of high temperature oxide (HTO), Si3N , SiO2, high temperature oxide (HTO), and boro- phosphate silicate glass (BPSG) atop a silicon substrate. Because HF reacts at different rates with the materials of the different layers, the resultant contact hole has a "jagged edge" wall structure. This uneven structure presents substantial difficulties when the contact hole is coated with a barrier layer, for example of tantalum nitride (TaN). The barrier layer of TaN is added to prevent metal ions, such as for example copper, from diffusing into the dielectric (SiO2) layers of the wafer. Metal atoms are a substantial source of leakage current. As TaN is coated on a surface, surface nonconformities tend to create discontinuities in the coating. These discontinuities may provide leakage paths for metal to enter the coated layers as shown in Figure 3. The effects of non-uniform contact hole side walls is magnified as device dimensions shrink.
SUMMARY OF THE INVENTION
The present invention provides a method and system for modifying the surface of a substrate such as a semiconductor device or wafer by atomic layer removal (ALR) and/or atomic layer exchange (ALEx).
Advantages of the present invention may be realized by the ALR and ALEx method and system described herein in which a method is provided for uniformly removing a layer of molecules of a first solid compound from a surface of a substrate. The substrate is exposed to a first reactive gas that reacts with a first layer of molecules on the surface to form a mono-layer of molecules of an intermediate solid compound on the surface. After removal of the first reactive gas from contact with the substrate, a second reactive gas is introduced. The second reactive gas reacts with the intermediate solid compound to form a volatile or volatihzable product. The second reactive gas and the volatile or volatihzable product are then removed from contact with the substrate which has one fewer molecular layers of the first solid compound on its surface.
In another embodiment of the present invention, a method of atomic layer exchange is provided. A film having multiple atomic layers formed on a substrate, and comprising at least one molecular layer of a first solid compound having at least a first and a second solid chemical species is exposed to a first reactive gas. The first reactive gas has at least a first and a second gas chemical species. A surface reaction occurs wherein the first solid chemical species is exchanged with the first gas chemical species to form an intermediate solid compound. In further embodiments of this aspect of the invention, the substrate is a second reactive gas which reacts with the intermediate solid compound to produce one or more volatile products, leaving the film of the first solid compound with one fewer molecular layers than it started with.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become apparent upon reading the detailed description of the invention and the appended claims provided below, and upon reference to the drawings, in which:
Figure 1 is a schematic diagram showing the effects of a prior art hydrofluoric acid bath etch treatment on a stack of different chemical layers.
Figure 2 is a schematic diagram showing the effects of a prior art hydrofluoric acid bath etch treatment on the walls of a contact hole through layers of different solid materials.
Figure 3 is a schematic diagram illustrating the effects of uneven contact hole walls resulting from prior art etch techniques on TaN barrier layer coating and the resultant diffusion of metal ions into SiO2 and Si3N layers on a semiconductor wafer. Figure 4 is a schematic view illustrating the steps of the atomic layer removal method according to one embodiment of the present invention.
Figures 5 A to 5D are schematic illustrations of the steps of an atomic layer removal method according to another embodiment of the present invention.
Figures 6A to 61 are schematic diagrams illustrating the steps of atomic layer exchange followed by atomic layer removal according to another embodiment of the present invention.
Figure 7 is a schematic diagram showing illustrating the improvement in side- wall uniformity relative to prior art methods resulting from treatment of a semiconductor wafer contact hole through layers of different solid materials using a method according to the present invention
Figure 8 is a schematic diagram illustrating the steps of an atomic layer removal technology according to the present invention, in which the silicon substrate is passivated to HF attack by creation of a H-terminated, hydrophobic surface prior to exposure to HF vapor, to uniformly remove a surface mono-layer of molecules from each of the layers in a wafer stack. Figure 9 is a flow chart outlining the steps of an atomic layer removal method according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an atomic layer removal and atomic layer exchange method and system. When referring to the removal aspect of the method, the abbreviation "ALR", for atomic layer removal, is often used. Additionally, the term atomic layer exchange "ALEx" may also be used to describe the method. The two processes are related as each method may be used to remove the surface layer of a solid compound from a substrate. ALEx can also be used to modify the surface of the In general the present invention provides an atomic layer removal and atomic layer exchange method and system where a substrate having a film deposited or grown on the surface of the substrate is placed in a reactor or chamber. A first reactant gas is introduced into the reactor or chamber to react with a first layer of the film to convert the first layer into a mono-layer of a solid compound. The reactor or chamber is purged to remove unreacted first reactant gas and/or any gas-phase products. A second reactant gas is then introduced into the reactor or chamber to react with the mono-layer of the solid compound to form a gaseous compound, which is removed from the reactor by a second purging step.
In one embodiment of the present invention, the first reactant gas may require the addition of a source of energy to activate or facilitate the reaction of the first reactant gas with the first layer of the film. The energy source may be in the form of electromagnetic radiation or some other energy delivery method. Examples of this electromagnetic radiation include, but are not limited to, visible light radiation, infrared radiation, ultraviolet radiation, microwave radiation, radio frequency radiation, and the like. The radiation may be supplied in a coherent form from a device such as a laser, or in a non-coherent (i.e. out of phase) form from a device such as a lamp. The use of the energy source will facilitate the reaction of the first reactant gas with the first layer of the film.
The present invention may be utilized for the removal of single atomic layers from the surface of the wafer. Additionally, the atomic layer removal process is a self terminating sequential atomic layer removal process. This process may be used to remove a wide variety of compounds from a surface prior to a subsequent deposition process. The removed compounds may comprise intentionally or incidentally deposited oxide coatings as well as solid substrate material and/or compounds deposited in layers by chemical vapor deposition, among others. The present invention may be used to reduce a deposited conductive or dielectric film thickness to achieve a desired final film thickness. These are just a few of the applications of the present invention.
In general, a first reactive gas is reacted with the top layer of a film to convert the top layer to a mono-layer of a solid compound. The first reactive gas is a chemical agent that converts an atomic layer of a fist solid compound in the surface film or upper layer of a substrate to a mono-layer of an intermediate solid compound which can be further reacted with a second reactive gas. The selection of the first reactive gas depends on the molecular composition of the film and the chemistry of the first solid compound. The mono-layer of the intermediate solid compound is then reacted with a second reactive gas to form a volatile or volatihzable product. This volatile or volatihzable product is removed by any suitable means which are well known in the art such as with an inert purge gas, with a vacuum pump, or with a combination of the two techniques. The above steps of this embodiment of the present ALR method can be summarized in the following equations:
A(S0lid) + B(gas) - D(Solid) (1)
D(solid) + C(gas) ~ E(Gas) T (2) where A(S0iid) is the first solid compound on the surface of the substrate, B(gaS) is the first reactive gas, D(s0iid) is the intermediate solid compound, C(gas) is the second reactive gas, and E(Gas) is the volatile or volatihzable product. Reaction steps(l) and
(2) can be repeated until the desired number of layers of molecules of A(S0iid) are removed from the substrate.
According to a more detailed embodiment of the method of the present invention that is illustrated in Figure 4, a substrate 10 having a film 12 deposited or grown on the surface of the substrate is placed in a reactor, chamber, or some other environment in which its exposure to a sequence of reactive gases may be controlled. The film is typically comprised of multiple atomic layers, in this example, of a first solid compound A(S0Hd). In this example, the film of A(S0Hd) is 3 molecular layers thick. However, any thickness of film and/or other solid or deposited surface compound may be treated according to the present invention. The number of molecular or atomic layers of the first solid compound present on the surface of the substrate may vary widely depending on the specific application. The first solid compound, A(SOiid to be removed may include any type of film used in semiconductor processing such as any gate dielectric or ceramic, to metal oxides, silicon oxides, metal aluminates, silicon aluminates, metal silicates, metal nitrides, silicon nitrides, pure metals or other films commonly found in semiconductor devices. In theory, any surface may be treated using the method of the present invention provided the proper reactive gases are chosen. The substrate 10 and film 12 shown in panel (I) are exposed to a first reactive gas B(gas). B(gas) is preferably a chemical agent that converts an atomic and/or molecular layer of the first solid compound A(SOiid) on the film or substrate surface to a mono-layer of an intermediate solid compound D(S0iid). Preferably the first reactant gas B(gas) is selected to react with the first solid compound A(soljd) to form a mono- layer of the intermediate solid compound D(S0Ud) on the substrate surface. The reaction of the first reactive compound B(gas) with the first solid compound A(SOud) is preferably either thermodynamically favored and/or kinetically favored relative to the reaction of the mono-layer of the intermediate solid compound D(SOiid)- hi other words, the reaction of the first reactive compound B(gas) with the clean A(SOiid) surface should result in formation of a uniform surface coated with a mono-layer of the intermediate solid compound D(soιid). Thermodynamically favored, as used above, means that the reaction of B(gas) with D(SOnd) according to
B(gas) + D(solid) - (3) is substantially less exothermic than reaction (1). Kinetically favored as used above indicates that reaction (3) proceeds at a substantially slower reaction rate than reaction (1). It is also preferable that the intermediate solid compound D(SOκd) forms a layer that retards contact between additional gas-phase molecules of the first reactive gas B(gas) with underlying layers of the first solid compound A(SOiid) so that only a mono- layer of D(Soiid) is formed. Examples of compounds for use as the first reactant gas B(gas) according to the present invention include but are not limited to: ozone, hydrogen, alcohols, water, ammonia, and the like.
As shown in panel (II) and discussed above, exposure to the first reactive gas B(gas) converts the surface layer 14 of first solid compound A(soij ) molecules to a mono-layer of intermediate solid compound D(son ). Excess first reactant gas B(gas) is evacuated from the reactor or chamber using a standard technique well known in the art such as with an inert purge gas, with a vacuum pump or the like, or with a combination of one or more such techniques. The substrate is then exposed to a second reactive gas, C(gaS), which converts the surface mono-layer of intermediate solid compound D(soljd) to a volatile or volatihzable product E(gas) as shown in panel (III). The second reactive gas C(gas) is preferably chosen such that its reaction with the mono-layer of intermediate solid compound D(soiid) is either substantially more exothermic (thermodynamically favored) or proceeds at a substantially faster reaction rate (kinetically favored) than the reaction of C(gas) with the film compound A(S0iid). hi other words, it is preferred that
C(gas) + A(S0iid) -> Y (4) where Y is some undesirable product, is substantially less exothermic than reaction (2) and/or that reaction (3) proceeds at a substantially faster reaction rate than reaction (4). hi this manner, treatment of a surface coated with a mono-layer of the intermediate solid compound D(aoiid) with the second reactive gas C(gas) results in the removal only of the mono-layer of the intermediate solid compound D(SOiid) without subsequent attack by the second reactive compound C(gas) on additional underlying layers of the first solid compound A(SOiid). hi one example, the second reactive gas C(gas) that reacts with the converted mono-layer of the intermediate solid compound D(soiid) may be a halogen containing source. Examples of halogen containing compounds applicable to this method include, but are not limited to C1F , NF , HF and chlorine. The volatile or volatihzable product E(gas) volatilizes or is volatilized from the surface to leave film 12 which, in the present example shown in Figure 4, then contains two molecular layers of solid compound A(S0Hd), one layer less than prior to treatment. The volatilized product E(gas) and any excess second reactive gas C(gas) are then removed/purged from the reactor in the same manner as described above for removal of the first reactive gas. Second, third, and additional layers of the first solid compound A(S0iid) may be removed from the film 12 by repeating the above steps until a desired number of layers remain on the substrate. Generally the first and second reactive gases are each introduced into the reactor or chamber for a period of time sufficient to react with one mono, or atomic/molecular, layer on the film. Exposure times for the first and second reactive gases are generally on the order of approximately one half to sixty seconds, or more specifically in the range of approximately one to two seconds.
Another embodiment of the present invention is illustrated in Figures 5 A to 5D. In this embodiment, the film or wafer surface is comprised of a first and a second solid compound, A and B respectively, as shown in Figure 5A. The wafer surface may contain a film, or may contain only silicon with a native oxide formed thereon. In this example, atomic layer exchange takes place, and the wafer is exposed to a gaseous precursor CD as shown in Fig. 5B. In the third step, shown in Figure 5C, a surface reaction and exchange of species occurs with the top layer on the wafer. In this example, the surface reaction converts the top layer to a mono-layer of solid compound AD(SOiid). A "waste" gaseous compound of CB(gas) is also formed which is removed or purged from the chamber as previously described and shown in Figure 5D. In this embodiment, the steps may be summarized by the following equation: AB(solid) + CD(gas) -» AD(soiid) + CB(gas) (5)
Many types of gaseous precursors or reactants may be employed with the method of the present invention, and will be selected based in part on the chemical composition of the film. Additional examples of gaseous precursors include, but are not limited to ozone, ammonia, water, hydrogen, hydrazine, alcohols, halogens, and the like. As described above, atomic layer exchange takes place between free radicals or molecules in the gas phase and the wafer or film or substrate surface. Diffusion of these gaseous precursors through the wafer surface may be controlled by a number of parameters, including temperature, pulse time, chamber pressure, molecule size and reactivity - to avoid multi-layer atomic exchange. Another embodiment of the method of the present invention is illustrated more specifically in Figures 6A to 61, which show sequential steps in detail, h this example, atomic layer exchange and atomic layer removal are carried out. First, atomic layer exchange is carried out to modify the chemistry of the film surface according to the following equation: CB(solid) + DE(gas) → CE(soiid) + DB(gas) T (6) where CB(SOκd) is The first reactive gas DE(gaS) is conveyed to the reactor or chamber as shown in Figure 6B. Next, the first reactive gas DE(gas) is optionally activated to form one or more first gas-phase radical species as shown in Figure 6C. As mentioned above, activation may take place by a variety of means, such as by temperature, energy pulse, electromagnetic radiation, and the like. For some first reactive gas DE(gas) species and reaction conditions, activation is not necessary for the reaction to proceed. Atomic layer exchange with the top layer of the film takes place. The resultant surface layer of the film is then an intermediate solid compound CE(soiid) as shown in Figure 5D. After exchange, the chamber or reactor is purged and the formed first gaseous by-product DB(gaS) as well as any unreacted first reactive gas
DE(gas) molecules or free radicals are removed from the chamber. The top layer of the film has now been converted to the intermediate solid compound CE(S0iid) as shown in Figure 6E.
Next, atomic layer removal is carried out to remove the top intermediate solid compound (CE(SOiid)) layer of the film as shown in Figures 6F to 61. In this example, a second reactive gas XY(gas) is selected such that the surface film layer of intennediate solid compound CE(so]jd) reacts with second reactive gas XY(gas) and additional layers of the first solid compound CB(S0iid) (layers underlying the mono-layer of the intermediate solid compound CE(S0iid) on the film) does not react with XY(gas). The second reactive gas XY(gas) may optionally be activated to form one or more second gas-phase radical species, such as by energy pulse, temperature, or electromagnetic radiation or other means as shown in Figure 6G. In this example, reaction products in the gas phase are:
CE(soiid) + XY(gas) → CX(gas) + EY(gas) (7) where CX(gas) and EY(gas) are a second and a third gaseous by-product, respectively. The reaction occurs and the gaseous by-products CX(gaS) and EY(gas) are formed and purged from the chamber as shown in Figures. 6H and 61. Thus, one atomic layer of the film of the first solid compound CB(S0Hd) has been removed. These steps may be repeated as many times as desired for additional atomic layer removal. The benefits of the method of the present invention are readily understood in contrast to prior art methods for removing native oxide from a contact hole. As shown in Figure 2, native oxide contamination at the bottom of a contact hole formed by reactive ion etch or some comparable method in a multi-layer stack of deposited substrate material may be removed via exposure of the substrate and multi-layer stack to a solution of hydrofluoric acid (HF bath). As shown and discussed above in regards to Figure 2, the removal of material from the exposed layer surfaces in a reactive etch bath is reaction rate limited, and the etchant reacts with different layer materials at different rates, so the traditional wet etch technique results in a non-planar sidewall after the etch. In one example of the present invention, the oxide layer at the bottom of a contact hole formed through a multi-layer stack of material is removed without formation of a non-planar hole. The present invention is used to remove the oxide at the bottom of the contact hole while maintaining the planarity of the sidewall. Because the method of the present invention uniformly removes a single mono-layer regardless of the reactivity of the surface compound in each reaction cycle, the process avoids the problems of kinetic-driven wet etching in which more reactive materials are etched away at faster rates than less reactive materials. In this example, water is used as the first reactant gas to form an — OH terminated surface on all of the exposed oxide surfaces. Dielectric films of silicon oxides and metal oxides are hydrophilic and this reaction proceeds easily. HF is then introduced as the second reactant gas and removes the top layer of the film in the form of water and SiF4 or metal fluoride. Generally, the reaction of HF with silicon oxides or metal oxides in the absence of water is very slow. Therefore, the reaction will self-terminate when the first layer is removed. This sequence can be repeated until the oxide at the bottom of the contact hole is removed. Since each cycle removes only one layer, regardless of the chemical nature of the oxide, the planarity of the sidewall will be retained.
The steps according to one embodiment of the present invention as shown in Figure 8 are (I) passivation of the non-oxide surfaces by exposure to hydrogen gas with UV activation, (II) introduction of water vapor (first reactive gas) or some other source, such as an alcohol, of hydroxyl ions and/or hydroxyl radicals, to change and standardize the surface state of the dielectric/oxide layers, (III) optional purging of the chamber/reactor to remove the water vapor, (TV) introduction of HF vapor to remove a surface layer of molecules for the dielectrics and oxides, and (V) repeat of steps (II)- (V) to remove additional layers as needed. As noted above, this technique is advantageous relative to the prior art HF etch method in which the substrate and dielectric layers are dipped in an aqueous bath of HF. The resulting non-uniform surface of contact holes and other surfaces featuring a number of different dielectric or oxide layers is avoided by the method of the present invention because the reaction of HF vapor with a hydroxylized surface proceeds only to remove the hydroxyl group (as water vapor) and its associated atom, as for instance SiF4 or A1F3 for SiO and Al O3, respectively. Once the oxide-HF reaction occurs once, the remaining non- hydroxylized surface is substantially less reactive to HF attack than the surface with attached hydroxyl groups.
Passivation of the hydrophobic surfaces, for instance Si, substantially retards HF attack of these regions because water vapor doe not substantially adsorb on the passivated regions (no hydrogen bonding) and therefore, the HF vapor does not react as strongly.
Figure 9 summarizes the steps of a method of ALR and/or ALEx according to the present invention. A substrate containing one or more films and/or solid compound layers is placed in a reactor, chamber, or other system for providing a controlled atmosphere to the surface in step 300. Any hydrophobic surfaces on the substrate may optionally be passivated by, for example exposing the substrate to hydrogen gas or some other compound that will react with surface oxide deposits to provide a surface that will not adsorb water vapor in step 302. This passivation step 302 may be activated by irradiating the gas mixture in the reactive atmosphere above the substrate with ultraviolet light sufficient to break molecular bonds in gas phase hydrogen or whatever passivating gas is used. The passivation step 302 also includes purging of the reactor or chamber to remove the passivating gas. Next, a first reactive gas is introduced to the atmosphere above the substrate in step 304. As noted above, the first reactive gas may be a source of oxygen such as for instance ozone, water, or an alcohol. Alternatively, the first reactive compound may be hydrogen or ammonia or some similar compound. The exact choice of a compound for use as the first reactive gas is made based on the desired intermediate reaction product and its reactivity with the chosen second reactive gas as discussed below. A knowledge of gas- and surface-phase chemistry characteristic of one of skill in the art and routine experimentation are sufficient to determine the proper combination of first and second reactive gases based on the substrate to be treated.
The first reactive compound may optionally be activated via electromagnetic radiation such as is discussed above or by some other energy input such as radiative, conductive, or convective heating in step 306. Depending on the reaction conditions, including but not limited to the substrate and film chemistry, temperature, and the like, some reactive gases may "self-activate" or react spontaneously with the film surface or interest. Whether the reaction is activated or not, the first reactive gas reacts with the surface mono-layer of the substrate surface to form a molecular layer of an intennediate solid compound in step 310. The first reactive gas is preferably chosen such that the reaction of the first reactive gas with the substrate or film surface proceeds to effective completion with the conversion of one surface layer of molecules from the starting solid compound to the intermediate solid compound. The first reactive gas does not further react with the intermediate solid compound, nor does the first reactive gas diffuse through the surface mono-layer of the intermediate solid compound to react with additional layers of the starting solid compound below the gas-solid surface. As noted above, these limitation can be either thermodynamic or kinetic. For example, the reaction of the first reactive gas with the intermediate solid compound is substantially less thermodynamically favored relative to the reaction of the first reactive gas with the starting solid compound. Alternatively, the rate of the reaction of the first reactive gas with the starting solid compound proceeds at a much faster rate than either the reaction of the first reactive gas with the intermediate solid compound or the reaction of the first reactive gas with layers of the starting solid compound that underlie the surface mono-layer of the intermediate solid compound.
After sufficient time for the reaction of the first reactive gas with the starting solid compound, the chamber or reactor is purged to clear any remaining gas from contact with the substrate in step 312. The length of exposure of the substrate to the first reactive gas depends on the kinetics and thermodynamics of the reaction, but is generally in the range of one to 60 seconds. Shorter reaction times of approximately half a second to one second may be used for very reactive gases. In general, however, the exposure time for the first reactive gas is in the range of approximately one to two seconds.
A second reactive gas is then introduced to the chamber or reactor in step 314. The second reactive gas is chosen such that its reaction with the intermediate solid compound formed in step 310 proceeds to effective completion by converting the intermediate solid compound to a higher vapor pressure compound or compounds that either volatilize from the substrate surface or are readily volatilized via some energy input such as heating. In one embodiment, the second reactive gas is a halogen- containing oxidizer compound. Suitable compounds include, but are not limited to C1F , NF3, HF, and chlorine gas. However, one of ordinary skill in the art may to select other compounds that are commensurate with the scope of the present invention based on the teachings provided herein.
As for the addition of the first reactive gas described above, the second reactive gas may optionally be activated by some energy input such as has been described above in step 316. Depending on the choice of the first reactive gas, the intermediate solid compound, and the second reactive gas, activation may or may not be necessary. The second reactive gas is exposed to the substrate for a reaction time in the range of approximately 0.5 to 60 seconds, with typical reaction times in the range of approximately one to two seconds. The second reactive gas reacts with the intermediate solid compound to convert the intermediate solid compound to a volatile or volatihzable product that either enters the gas phase immediately upon its formation or is readily evaporated from the surface in step 320. The second reactive gas is preferably selected to react substantially only with the compound of the intermediate solid compound formed as a mono-layer in step 310. The limitation on the reaction of the second reactive gas with the starting solid compound maybe either kinetic or thermodynamic as described above in regards to the first reactive compound. Preferably, the reaction of the second reactive gas with the starting solid compound is substantially less thermodynamically favored than that of the second reactive gas with the intermediate solid compound. Alternatively, the rate at which the reaction of the second reactive gas with the intermediate solid compound proceeds is substantially faster than the rate at which the reaction of the second reactive gas with the starting solid compound proceeds. If the volatile or volatihzable product does not substantially evaporate from the substrate surface upon formation, energy or some other evaporative inducement is provided via radiation, heat, or some other known technique to cause the volatile or volatihzable product to be released to the gas phase in step 322. Gas phase volatilized product and any excess second reactive gas are then purged from the chamber in step 324. For removal of additional molecular layers from the substrate, steps 304-324 may be repeated multiple times. In general, the optional passivation step is only used at the start of the process. Subsequent layers may be removed without re-passivating.
In another embodiment, the method of the present invention can be used to deposit an ultra thin film on a substrate with tightly controlled dimensions. For instance, prior art deposition technology has limitations in depositing a dielectric film having an ultra-thin thickness, such as a thickness of 3 A. With the method of the present invention, a dielectric film having a thickness of, e.g. 10 A can be first deposited on the surface of a substrate. Then layers of the dielectric films can be removed from the substrate using the atomic layer removal method as described above. There is no limitation on the number of layers to be removed. Thus, if a dielectric film with a thickness of 3 A is desired, then layers of a thickness of 7 A of the dielectric film can be removed by repeating the steps as described above, leaving a film with a thickness of 3 A remaining on the surface of the substrate.
The atomic layer removal and atomic layer exchange method of the present invention has broad applications. For example, the present invention can be used to etch metals and dielectrics, generate photolithographic masks, and improve resolution of liquid crystal displays, among other applications. Additionally, atomic layer removal of the present invention may be used for reducing final film thicknesses and/or removing undesired surface roughness prior to forming gate electrodes. The silicon - high K dielectric interface may be controlled by atomic layer exchange of the present invention along with low temperature ALD high K dielectric processes.
THEORETICAL EXAMPLE
The following theoretical examples illustrate the method and system of the present invention. These examples are intended for illustration purposes only, and are not intended to limit the scope of the present invention in any way.
Example 1
In one illustrative example, a layer of titanium nitride (TiN) is provided, and the removal to a desired thickness is achieved by the method and system of the present invention. Titanium nitride (TiN) is a preferable material for gate electrode barrier. To deposit a thin TiN film on a substrate, a relatively thick TiN film can be pre-deposited on the surface of a gate dielectric. According to this embodiment of the present invention, ozone gas is introduced to convert the top atomic layer of TiN film to a mono-layer of titanium dioxide (TiO2). The solid TiO layer is then further reacted with hydrogen fluoride (HF) vapor to form gaseous titanium fluoride (TiF4) and water, which are removed from the reactor. Each cycle of the method can remove one atomic layer of TiN from the substrate. By repeating the process, an ultra thin TiN film of a desired thickness can be achieved on a silicon substrate. There is no limitation on the number of TiN layers that can be removed by the atomic layer removal method of the present invention. Example 2 hi another example, ethanol is used as a first reactant gas to react with silicon dioxide (SiO2) film pre-deposited on a substrate. A mono-layer of silicon hydroxide (SiOH) is formed on the top surface of the substrate. Hydrogen fluoride (HF) is used as a second reactant gas to react with the solid silicon hydroxide to form gaseous silicon fluoride (SiF4) and water, which are removed from the reactor.
The foregoing description of specific embodiments and examples of the invention have been presented for the purpose of illustration and description, and although the invention has been illustrated by certain of the preceding examples, it is not to be construed as being limited thereby. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications, embodiments, and variations are possible in light of the above teaching. It is intended that the scope of the invention encompass the generic area as herein disclosed, and by the claims appended hereto and their equivalents.

Claims

CLAIMSWhat is claimed is:
1. A method for removing a layer of molecules or atoms of a first solid compound from a surface of a substrate, comprising the steps of: exposing said substrate to a first reactive gas, said first reactive gas reacting with a first layer of molecules on said surface to form a mono-layer of molecules of an intermediate solid compound on the surface; removing said first reactive gas from contact with said substrate; exposing said substrate to a second reactive gas, said second reactive gas reacting with said intermediate solid compound to form a volatile or volatihzable product; and removing said second reactive gas and said volatile or volatihzable product from contact with said substrate.
2. The method according to claim 1, further comprising the step of activating said first reactive gas to form one or more first gas-phase radical species.
3. The method according to claim 1, further comprising the step of activating said first reactive gas to form one or more second gas-phase radical species.
4. The method according to claim 1, further comprising the step of passivating one or more areas on the surface of said substrate.
5. The method according to claim 4 wherein said passivating step comprises the steps of exposing said substrate to hydrogen gas; and irradiating said hydrogen gas with ultraviolet light to form free-radical hydrogen atoms, said free-radical hydrogen atoms reacting with said one or more areas.
6. The method according to claim 1 wherein said first reactive gas is a source of hydroxyl ions and/or hydroxyl radicals.
7. The method according to claim 1 wherein said first reactive gas is chosen from the group consisting of water vapor, alcohol, ozone, ammonia, and hydrogen.
8. The method according to claim 1 wherein said second reactive gas is a halogen-containing compound
9. The method according to claim 1 wherein said second reactive gas is chosen from the group consisting of C1F3, NF , HF, and Cl2.
10. The method of any of claims 1 to 9 wherein the reaction of said first solid compound, A(Solid) with said first reactive gas B(gas) to form said intermediate solid compound D(Soiid) occurs according to:
A(Soiid) + B(gas) -» D(soiid) (1) and the reaction of said intermediate solid compound, D(S0ud) with said second reactive gas C(gas) to form said volatile or volatihzable compound E(Gas) occurs according to:
D(solid) + C(gas) - E(Gas) (2).
11. The method according to claim 10 wherein the reaction of said first reactive gas B(gas) with said intermediate solid compound D(s0iid) to form undesirable product X occurs according to: B(gas) + D(SOiid) -» X (3) and reaction (3) is substantially less thermodynamically favorable than reaction (1).
12. The method according to claim 10 wherein the reaction of said first reactive gas B(gas) with said intermediate solid compound D(s0iid) to form undesirable product X occurs according to:
Figure imgf000021_0001
and the reaction rate of reaction (3) is substantially slower than the reaction rate of reaction (1).
13. The method according to claim 10 wherein the reaction of said second reactive gas C(gas) with said first solid compound A(s0ud) to form undesirable product Y occurs according to:
C(gaS) + A(Solid) - Y (4) and reaction (4) is substantially less thermodynamically favorable than reaction (2).
14. The method according to claim 10 wherein the reaction of said second reactive gas C(gas) with said first solid compound A(s0iid) to form undesirable product Y occurs according to:
Figure imgf000022_0001
and the reaction rate of reaction (3) is substantially slower than the reaction rate of reaction (1).
15. The method according to claim 1 wherein the reaction of said first solid compound, CB(soiid) with said first reactive gas DE(gas) to form said intermediate solid compound CE(S0Hd) and a volatile product gas DB(gas) occurs according to:
CB(soiid) + DE(gas) → CE(Soiid) + DB(gas) t (6) and the reaction of said intermediate solid compound, CE(SOiid) with said second reactive gas XY(gas) to form said volatile or volatihzable compound CX(oas) and a second volatile or volatihzable compound EY(Gas) occurs according to:
CE(solid) + XY(gas) → CX(gas) + EY(gas) (7)
16. The method of Claim 1 wherein said first solid compound is comprised of a dielectric, ceramic, metal oxide, metal, semiconductor, or polymer material.
17. A method for preparing a thin film of a deposited compound on a substrate comprising the steps of depositing a layer of said deposited compound on said substrate, said deposited layer comprising at least two molecular layers of said deposited compound; and removing one or more molecular layers from said layer using a method according to any of claims 1 to 16.
18. A method of atomic layer exchange with a film having multiple atomic layers formed on a substrate, characterized in that: the film, said film comprising at least one molecular layer of a first solid compound having at least a first and a second solid chemical species, is exposed to a first reactive gas, said first reactive gas having at least a first and a second gas chemical species, and where a surface reaction occurs wherein the first solid chemical species is exchanged with the first gas chemical species to form an intermediate solid compound.
19. The method according to claim 18 wherein the reaction of said first solid compound, AB(SOiid) with said first reactive gas CD(gaS) to form said intermediate solid compound AD(soiid) and a volatile product gas CD(gas) occurs according to:
AB(solid) + CD(gas) → AD Soκd) + CB(gas) (5)
20. The method according to claim 18 further characterized in that said substrate is exposed to a second reactive gas which reacts with said intermediate solid compound to convert said intermediate solid compound into at least one volatile product and wherein said second reactive gas does not substantially react with said first solid compound.
21. Independent claim to method shown in figure 7
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