Specific Process Knowledge/Thin film deposition/DiamondCVD

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SEKI Diamond CVD

On the left is a tall instrument rack with various panels and control screens. It says "Seki technotron" on top. There are indicator lamps and an EMO button. On the right is the processing chamber which is relatively small, it's a cylindrical vacuum chamber with a small window facing the viewer. It's connected to gas lines and an exhaust system on top. There's a large panel covering the lower part of the instrument.
The SEKI diamond CVD in cleanroom B-1

The SEKI AX5250S is a Microwave Plasma Chemical Vapor Deposition (MPCVD) system for growth of diamond thin films. The system is fitted with gases for diamond growth, which are hydrogen, methane, and oxygen.

Depending on the starting material both polycrystalline and single crystalline diamond can be grown. Diamond has a lattice constant of 3.567 Å, which is not easily matched to other materials, and therefore in general diamond growth must be seeded by diamond as nucleation sites.

For single crystalline diamond this means that diamond layers in most cases must be grown on top of single crystal diamonds. For polycrystalline diamond, almost any material (which can handle 800 °C) will do. It just needs to be seeded with nano diamonds. The seeding can happen by immersion into solution, by polishing, or by spray coating with nano diamonds.

The user manual, APV, technical information, and contact information can be found in LabManager:

Diamond CVD in LabManager


Diamond growth

Structural formula diagrams of the growing diamond lattice showing how a hydrogen radical knocks off a hydrogen atom that terminates the diamond lattice, then a methane radical attaches to the activated site. The same thing happens at an adjacent site and finally one hydrogen radical after another knock off two hydrogen atoms on the recently-attached methane sites to create a new single carbon-carbon bond. The two new carbon atoms are also still bound to two hydrogen atoms each.
Structural formula diagrams of diamond growth

Diamond is grown by depositing carbon from the CH4 on a substrate. If the carbon forms an sp3 bond to other carbon atoms, diamond is grown. Otherwise it will be etched away by a high concentration of H2. Diamond is very inert, but the plasma in the CVD equipment creates hydrogen radicals that in turn create active sites on the diamond surface. These active sites react with methane radicals that are also created in the plasma.

3D-image of the Diamond crystal lattice. Each carbon atom is bound to the four nearest carbon atoms via sp3 hybridization. On the left you see an extended diamond lattice. On the right you see a carbon atom with four sp3 hybrid orbital lobes extending from the center with an angle of 109.5 degrees between the lobes.
Diamond bonding



Single- and polycrystalline diamond

Two-inch wafer that has a speckled dark gray appearance with three small transparent partly overlapping squares in one area on top. The wafer is labeled as "polycrystalline diamond substrate" and the squares are labeled as "single crystal diamond"
Single- and polycrystalline diamond

It is possible to grow extremely clean diamond in the SEKI system. It is also possible to control the N2 dopant level and dopant depth. Nitrogen doping affects the optical and electronic properties of the diamond. For instance this can be used in magnetic sensors, which is a topic of research at DTU Physics.

For polycrystalline growth the substrate must be seeded with diamonds as mentioned above. This is commonly done by sonicating the substrate in a solution of water with nano diamonds. After sonication the substrate is rinsed in water and blow-dried.

Polishing is needed after deposition if the polycrystalline diamond layer has to be smooth. Thinning is needed if the diamond layer has to be very thin as a uniform diamond layer can only be deposited above 1 μm thickness.


Equipment performance and process related parameters

Equipment SEKI AX5250S
Purpose Diamond growth
  • Single crystalline diamond
  • Poly crystalline diamond
Parameters

H2

1000 sccm

CH4

50 sccm

O2

20 sccm

Operating pressure

>200 Torr

Power

5000 W

Temperature

700-900 °C

Process Growth rate

About 8 Å/s (3 μm/hr)

Max thickness

About 100 μm

Uniformity

OK up to 50 mm diameter
1 μm thickness needed to ensure substrate coverage

Substrates Substrate size

up to 100 mm wafers, 50 mm preferred

Allowed materials

Ask


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