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Material World
Process

Vapour deposition

Building a solid layer out of a gas, an atom at a time — how every thin film is made, from a touchscreen electrode to a synthetic diamond.

Vapour deposition covers a family of methods that all do the same thing: deliver a material to a surface as individual atoms or molecules and let it build up there as a solid. The film that results can be a few atoms thick or a few microns, follows the surface exactly, and can be made of things that cannot be melted, rolled or cast at all.

The division within the family is whether a chemical reaction is involved. Chemical vapour deposition supplies gases that react at the hot surface and leave the wanted solid behind; physical methods — evaporation, and sputtering, in which ions knock atoms off a target — move the material without changing it.

Processing

Sputtering is the workhorse of the coating industry. A target of the material is bombarded with argon ions in a vacuum, atoms are ejected, and they condense on whatever is placed opposite. It works for metals, oxides and alloys alike, it keeps the target's composition in the film, and it coats the large glass sheets that displays and low-emissivity windows are made from.

Chemical vapour deposition reaches where sputtering cannot. Because the film is formed by a reaction rather than delivered as a beam, it coats surfaces the source cannot see — the inside of a tube, the walls of a trench a hundred nanometres wide — which is why every semiconductor process depends on it.

Its most striking product is diamond. Methane and hydrogen in a plasma, at a pressure far below the one diamond is supposed to need, deposit carbon on a seed in the diamond arrangement rather than the graphite one — the hydrogen etching away graphite faster than diamond as it forms. Diamond grown at low pressure was thought impossible for most of a century.

Economic significance

Almost every coated thing is coated this way. Hard coatings on cutting tools, the low-emissivity layer in double glazing, the transparent electrode in a touchscreen, the reflective layer in optics, and every conducting and insulating layer inside an integrated circuit.

CVD diamond has quietly changed two markets. It supplies optical windows and heat spreaders that no other material can, and it has made gem-quality diamond a manufactured product — which the natural diamond trade has responded to with detection equipment rather than with argument, since the two are chemically and structurally the same thing.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

produces

  • Indium tin oxide — material · sputtered onto glass in sheets, which is the only way to make a transparent electrode over square metres
  • Cadmium telluride — compound · deposited straight onto glass in a continuous line — the reason a thin-film panel is cheaper to make than a silicon one is that it is never a wafer
  • Diamond — mineral · as CVD diamond, grown from methane and hydrogen in a plasma at a pressure far below the one diamond was supposed to need — and chemically and structurally identical to the mined mineral
  • Silicon carbide — compound · as the epitaxial layer that a silicon carbide power device is actually built in, on top of a wafer made the harder way
  • Optical fibre — material · the preform is built by burning silicon and germanium chlorides to deposit soot layer by layer, which is why the glass is pure enough to see through kilometres of — transition metals do not survive the vapour route
  • Gallium nitride — compound · and it has to be: GaN decomposes rather than melting, so it cannot be pulled from a melt the way silicon is and must be grown atom by atom from vapour onto a foreign substrate
  • Polysilicon — material · the Siemens process: trichlorosilane distilled to purity, then decomposed onto heated silicon rods at 1,100 °C until they grow thick enough to break up
  • Silicon nitride — compound · as the thin film on a solar cell and a chip; the bulk ceramic is made instead by nitriding silicon powder and sintering it

is used in

  • Semiconductor manufacturing — industry · every conducting and insulating layer inside an integrated circuit is deposited, because none of them can be placed any other way

succeeded

  • Czochralski process — process · the boule makes the substrate; deposition makes everything on top of it

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Vapour deposition back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Downstream — what it becomes

  • Vapour deposition → produces (the Siemens process: trichlorosilane distilled to purity, then decomposed onto heated silicon rods at 1,100 °C until they grow thick enough to break up) → Polysilicon → is an input to (melted and pulled into the single crystal the wafers are sliced from — polysilicon is the feedstock, and the puller changes its arrangement rather than its purity) → Czochralski process → produces (as the single-crystal wafer every integrated circuit is built on — the metallurgical grade that comes out of a furnace is the same substance and not remotely the same thing) → Silicon → is used in (the substrate of essentially all of it, and it won not on being the best semiconductor but on forming a stable insulating native oxide) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Vapour deposition → produces (sputtered onto glass in sheets, which is the only way to make a transparent electrode over square metres) → Indium tin oxide → is used in (the transparent electrode of the touchscreen, which has to conduct and be invisible at the same time — a combination almost nothing offers) → Smartphone → is used in (and it is where four separate raw-material arguments meet — the 3TG conflict minerals, cobalt, the rare earths, and everything too dispersed to recover) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Vapour deposition → produces (and it has to be: GaN decomposes rather than melting, so it cannot be pulled from a melt the way silicon is and must be grown atom by atom from vapour onto a foreign substrate) → Gallium nitride → is used to make (as the high-electron-mobility transistor that has taken most of the high-power radio-frequency market — 5G base stations, radar and satellite transmitters) → Transistor → is used in (the component every other modern technology is assembled from, and one nobody ever sees) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Vapour deposition → produces (as the epitaxial layer that a silicon carbide power device is actually built in, on top of a wafer made the harder way) → Silicon carbide → is a component of (where abrasion and thermal shock both matter — blast furnace bosh, incinerators and kiln furniture) → Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (fired in a continuous tunnel kiln, the atmosphere governing colour as much as the temperature) → Brick → is used in (load-bearing walls and cladding) → Construction
  • Vapour deposition → produces (as the thin film on a solar cell and a chip; the bulk ceramic is made instead by nitriding silicon powder and sintering it) → Silicon nitride → is used in (the antireflective coating, and the reason panels are blue) → Solar panel → is used as (and the price fell roughly ninety-nine per cent in thirty years on thinner wafers, finer saws and rising cell efficiency) → Photovoltaics
  • Vapour deposition → produces (deposited straight onto glass in a continuous line — the reason a thin-film panel is cheaper to make than a silicon one is that it is never a wafer) → Cadmium telluride → is used as (the only thin-film technology to have taken and held real market share from silicon) → Photovoltaics

These are the most distinct paths onward. Vapour deposition ends up in others besides.