Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
  • C30B23/02—Epitaxial-layer growth
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/18—Epitaxial-layer growth characterised by the substrate
  • C30B25/20—Epitaxial-layer growth characterised by the substrate the substrate being of the same materials as the epitaxial layer
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/08—Germanium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/24—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials using chemical vapour deposition [CVD]
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/27—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials using selective deposition, e.g. simultaneous growth of monocrystalline and non-monocrystalline semiconductor materials
  • H10P14/271—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials using selective deposition, e.g. simultaneous growth of monocrystalline and non-monocrystalline semiconductor materials characterised by the preparation of substrate for selective deposition
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/27—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials using selective deposition, e.g. simultaneous growth of monocrystalline and non-monocrystalline semiconductor materials
  • H10P14/276—Lateral overgrowth
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/29—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials characterised by the substrates
  • H10P14/2901—Materials
  • H10P14/2902—Materials being Group IVA materials
  • H10P14/2905—Silicon, silicon germanium or germanium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/32—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials characterised by intermediate layers between substrates and deposited layers
  • H10P14/3202—Materials thereof
  • H10P14/3204—Materials thereof being Group IVA semiconducting materials
  • H10P14/3211—Silicon, silicon germanium or germanium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/32—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials characterised by intermediate layers between substrates and deposited layers
  • H10P14/3242—Structure
  • H10P14/3256—Microstructure
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/34—Deposited materials, e.g. layers
  • H10P14/3402—Deposited materials, e.g. layers characterised by the chemical composition
  • H10P14/3404—Deposited materials, e.g. layers characterised by the chemical composition being Group IVA materials
  • H10P14/3411—Silicon, silicon germanium or germanium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P14/00—Formation of materials, e.g. in the shape of layers or pillars
  • H10P14/20—Formation of materials, e.g. in the shape of layers or pillars of semiconductor materials
  • H10P14/34—Deposited materials, e.g. layers
  • H10P14/3402—Deposited materials, e.g. layers characterised by the chemical composition
  • H10P14/3414—Deposited materials, e.g. layers characterised by the chemical composition being group IIIA-VIA materials
  • H10P14/3421—Arsenides

Definitions

• the present invention relates to a method of producing layers of germanium and other materials, principally on silicon substrates.
• WO-A-99/19456 discloses theoretical investigations for growing threading dislocation-free hetero epitaxy.
• the proposed method involves forming on an Si substrate a layer of a material with a different lattice constant. This creates bumps in the layer, known as Stranski-Krastanov islands, arising from buckling of the layer under strain. Dislocations around the bumps are removed, allowing further defect-free growth of the islands, eventually to form a continuous layer.
• This is essentially a theoretical analysis, and there is no evidence that the method has been, or could be, implemented in practice, since the resultant structure has an interface between two materials of different lattice constant. This would result in immense strains set up at the interface, with no means of relieving the strains.
• the present invention provides a method of producing a layer of a desired material, the method comprising: a) providing a substrate of silicon, having a different lattice constant from said desired material, and depositing said desired material on the substrate such that rounded protuberances are produced; b) filling the areas between the protuberances with a non-crystalline material; and c) depositing again said desired material, the rounded protuberances serving as growth sites whereby to produce a layer of said material.
• the invention provides a semiconductor structure comprising a substrate of silicon, protuberances of a desired material formed on the substrate surface, said protuberances having a rounded shape, and the desired material having a different lattice constant from that of silicon, a layer of non-crystalline material being formed between the protuberances, and a layer of said desired material being formed on top of, and in contact with, the rounded protuberances.
• the layer of material is essentially formed in step c) as single crystals extending from each protuberance.
• the crystals may extend to form a more or less continuous layer; alternatively the growth may continue to form a layer of uniform thickness.
• the protuberances may be formed on the substrate in any desired way.
• the substrate may be prepared to define sites on which the desired material may be deposited, by lithography or other methods (for example, that described in our copending applicationWO 01/84238).
• SK Stranski Krastanov
• the growth of the initial layer is carried out in steps of pre-determined duration, as described in more detail below, so that only rounded bumps remain and substantially all the pyramidal shaped bumps no longer exists.
• the advantage of using larger rounded bumps is that the lattice spacing at the top of the bump is substantially that of the desired material, since the lattice structure at the top of the bump is substantially relaxed.
• the material preferably comprises germanium.
• the germanium may be replaced by a suitable alloy of germanium and silicon, Ge x Si 1-x .
• the substrate on which the germanium layer is formed is silicon, since silicon is a very cheap material and can be produced in wafers approaching 12 inches wide.
• substrates other than silicon may be employed.
• the present invention is very suitable for use as a compound solar cell comprising Ge/GaAs/GalnP. Solar cells do not require a single crystal formation in the layer of germanium, i.e. pure epitaxial growth of the germanium layer. Solar cells will function perfectly adequately with polycrystalline growth, i.e.
• Figures 2, 3 and 4 are views of the rounded protuberances formed in step 1 of Figure 1;
• Figures 5 and 6 are views in crossection of a germanium layer formed on a silicon substrate by the process of Figure 1 ;
• Figure 7 is an enlarged view of a germanium protuberance with epitaxial growth of a layer of germanium thereon.
• Figure 8 shows four sequential steps diagrammatically in the production of a germanium layer in accordance with a second embodiment of the invention. Description of the Preferred Embodiments
• self-assembled Ge-dots are produced on Si(001) substrates in UHV-CVD, a stable oxide mask (SiO ) will be created in the area between the dots, the GeO on top of the Ge-dots will be reduced by H 2 and finally, the Ge-dots are used as the seeds for epitaxial lateral overgrowth of the SiO 2 with Ge.
• the whole process is based on self-organisation, i.e. no special processing steps will be necessary.
• the result will be a structure of Ge (or Ge x Si ⁇ _ x ) on Si.
• the formed Ge-layer can be thin and can be a base for further deposition of, for instance, GaAs/GalnP on top of it.
• a thin layer of germanium is formed on a silicon substrate having a face on the ⁇ 001> plane under ultrahigh vacuum conditions by a chemical vapour deposition process.
• self-assembled SK pyramidal-shaped dots 14 are formed in the germanium layer, between 4 and 6 nanometers high.
• these dots Upon continued growth, these dots have a rounded form and are between 12 and 20 nanometers high, and between 60 and 100 nanometers wide.
• UHV- CVD ultra-high vacuum chemical vapour deposition
• a step-wise growth mode consisting of two Ge deposition steps with a short growth interruption in between.
• a “base structure” with pyramids and domes is grown while in the second one an additional Ge amount at reduced pressure is supplied.
• Selective “feeding” of only the pyramids and their conversion into domes occurs
• Both, pyramids and domes are coherent (i.e. dislocation free) islands.
• Superdomes are the largest, no longer coherent islands, that have ⁇ 111 ⁇ facets and other facets in addition at the boundary with the substrate.
• the islands go through shape transitions from pyramids to domes or domes to superdomes.
• the spontaneously formed 3 -dimensional (3D) islands show a bimodal size distribution, containing pyramids and domes coexisting even for long times of annealing.
• the dots produced have a lattice constant at the silicon substrate corresponding to that of silicon, but as the germanium extends away from the substrate, the strain in the germanium lattice gradually relaxes so that at the top of the dots, the lattice constant approaches that of germanium.
• the lattice dimensions of the top layer are equal to that of the natural lattice constant of germanium without strain. Therefore no dislocations are produced.
• the protuberances have a bimodal size distribution, with smaller protuberances having a generally pyramid profile and growing to a height of up to 6 nanometers.
• the rounded protuberances grow to a greater height. It is desired to ensure that all the pyramid-shape protuberances are removed.
• the pyramid protuberances are enlarged in a second step of germanium deposition wherein germanium is deposited for a short time period of 57 seconds at a pressure of 2 X 10 ⁇ 4 mbar, then followed by deposition at 1.1 X lo nbar for a time period of 8 seconds.
• Figure 3 is a further view of the bimodal distribution, with a lower density of pyramids.
• FIG 4 is a view of the protuberances, with the pyramids essentially removed.
• the substrate and germanium layer are oxidised by applying a nitrogen gas saturated with water at a temperature of 500°C for 0.5 hours.
• This oxidises the germanium layer to produce germanium dioxide, and also oxidises the underlying silicon substrate in the regions between the protuberances to produce silicon dioxide. Since the silicon dioxide expands, the resultant structure as shown in Figure 1 has regions 20 full of silicon dioxide between the dots 14 and an overlying layer of germanium dioxide 22.
• the oxidation effect of germanium is small since germanium forms a wetting layer at the surface with a thickness of only a few monolayers
• step 3 a reduction process is carried out wherein the germanium dioxide is reduced by application of hydrogen.
• the result as shown in Figure 1C is to produce germanium dots or protuberances 14 surrounded by islands of amorphous silicon dioxide 30.
• Reduction by hydrogen at temperatures below 800°C does not attack the silicon dioxide layer because of the higher thermo chemical stability of silicon dioxide. Since these amorphous regions 30 do not provide a lattice construction to which germanium will register, a further deposition process of germanium by MOCVD, as shown in Figure ID, step 4, will produce germanium nucleating on the germanium protuberances 14 and extending between protuberances to produce a layer of germanium 40 of perfect crystallinity.
• Step 1 self-assembling Ge-dots: The growth of almost uniform dome-shaped Ge-islands on Si(001) according to figure 1A, step 1, was performed by a two-step growth procedure using ultra-high-vacuum chemical vapor deposition (UHV-CVD). Silane (SiE ) and germane (GeELi, 10% diluted in H 2 ) were used as source materials. We used substrates cleaved from (001) oriented n-doped Si wafers. First the samples were cleaned in organic solvents and sonicated in ultrasound bath.
• UHV-CVD ultra-high-vacuum chemical vapor deposition
• Step 2 surface oxidation: This step (figure IB) is to perform under very gentle conditions . The best results were obtained by taking off the sample from the reactor cell, exposing it to air at room-temperature for 60 min and putting it back to the reactor.
• the native oxide which grows under such conditions on the surface is about 2 nm thick. It covers also the Ge-dots, whereby due to the incorporation of Si as an impurity into the dots the formed oxide is a mixture of GeO x and SiO x .
• Step 3 selective reduction: This step (step 3 in figure 1C) was done in the UHV-reactor cell at a temperature of 600 °C by filling the cell with H 2 over a time of 60 min. The reduction process started with a H 2 -pressure of 0 and was then linearily ramped up to 600 Torr at the end of the reduction process. Subsequently, the H 2 was pumped away.
• Step 4 epitaxial lateral overgrowth: This step (step 4 in figure 1) was done immediately after step 3 had finished and the H 2 was pumped out of the reactorcell down to a pressure of ⁇ lxl0 " mbar. After this the GeH 4 was switched on and the nucleation of Ge on top of the former Ge-dots started. In order to restrict the Ge- nucleation to only areas where single-crystalline Ge phases can act as the seeds the GeH 4 -pressure for the first 10 min of deposition was kept on a low value of 2x10 "6 mbar. In order to deposit thicker layers the GeFLi-pressure was finally increased to ⁇ . ⁇ xlO "4 mbar for further 50 min of deposition.
• Fig. 5 is a Scanning Electron Micrograph (SEM) image of the cleavage plane.
• the bright layer 50 is Ge.
• Fig. 6 is a Transmission Electron Micrograph (TEM) image of a similar area.
• the dark layer 60 is Ge.
• the dark stripe 62 close to the Si-surface (about 45 nm away from the Ge) is caused by some Ge incorporation at the beginning of deposition (a memory effect from previous runs).
• Figure 7 shows, a single-crystalline deposition 70 of Ge on top of an oxidized/reduced/overgrown Ge-dot 72.
• the nucleation started in the area marked with a circle 74.
• lateral overgrowth of the oxide 76 occurs.
• the oxide comes from the contamination of Ge-dots with Si, i.e. it is mainly SiOx which does not reduce in the H2-atmosphere.
• the epitaxial information between the former Ge-dot and the deposited Ge is transferred close to the top of the former dot.
• the lattice planes of the single-crystalline Ge-rich material 70 penetrate the oxide layer 76.
• step 4 germanium is grown on the tops of the rounded domes by epitaxial lateral overgrowth.
• the area of deposited germanium extending from each dome site forms a single crystal. Since the intended application of the germanium layer is for a solar cell, only vertical movement of the electrons in the germanium layer is of interest between the various layers other solar cell. Therefore it is not necessary for the single crystals extending from each dome site to coalesce with adjacent crystals from adjacent dome sites in order for the solar cell to work properly. Therefore in this embodiment the upper layer of germanium comprises regions of single cells which more or less cover the entire area of the substrate and form a layer.
• Figure 5E shows a schematic view of a completed solar cell incorporating the second embodiment.

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• 2001
  • 2001-05-08 GB GBGB0111207.7A patent/GB0111207D0/en not_active Ceased
• 2002
  • 2002-04-30 CA CA002445772A patent/CA2445772A1/en not_active Abandoned
  • 2002-04-30 JP JP2002587677A patent/JP2004531889A/ja active Pending
  • 2002-04-30 EP EP02769150A patent/EP1386025A1/en not_active Withdrawn
  • 2002-04-30 US US10/477,130 patent/US6958254B2/en not_active Expired - Fee Related
  • 2002-04-30 WO PCT/GB2002/001980 patent/WO2002090625A1/en not_active Ceased

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