The role of vacuum in lab grown diamond production

Mention diamonds and most people will associate that with the jewelry sector. They will also have in mind that such gems are to be found in mines and sometimes won under severe conditions (“blood diamonds”). For such reasons, the industry already investigated in the 1950s how to produce synthetic diamonds.

Today, there are several processes available to create artificial diamonds or lab grown diamonds. Not only for jewelry where even experts are challenged to differentiate a natural diamond from an artificial, but also for the much larger market for diamonds in the industrial sector. Paul Zimnisky, CFA from Paul Zimnisky Diamond Analytics (www.paulzimnisky.com) has published the following analysis:

Four outstanding properties of synthetic diamonds

The key properties of synthetic diamonds that make them so interesting for the industrial sector are:

• Mechanical (superior hardness a chemical inertness)
• Optical (high transparency)
• Electrical (semiconductor properties)
• Thermal (highest heat conductivity)

Some typical industrial application examples are machining and cutting tools, window material for transmitting infrared and microwave radiation, and heat sinks for lasers and transistors. Synthetic diamonds are also the base material for semiconductor wafers and Qubits for quantum computing.

If you are interested to learn more in 2021 Awadesh Mallik, Ph.D. ? M.B.A. published a book called Engineering Applications of Diamond (ISBN 978-1-83968-532-3) examining the properties, advantages, and potential applications of diamonds in engineering and other fields.

How are diamonds obtained?

Traditionally diamonds were naturally formed billions of years ago in the earth’s crust by carbon atoms being exposed to intense heat and pressure. However, due to technical advances, a new source of synthetically grown diamonds was created. This market can be divided into 2 main manufacturing methods:

1. HPHT (High-Pressure High Temperature)– This method is based on how diamonds were naturally formed - compress carbon and add heat. The equipment footprint often has large and limited process control.
2. CVD (Chemical Vapor Deposition)– This method is based on creating a vacuum environment and then introducing specific gasses to trigger a reaction. The equipment footprint often has a small and excellent process control.

MPCVD (Microwave Plasma CVD) growing process

Due to its small footprint and excellent process controls, the MPCVD growing process has gained in popularity. One important part of the MPCVD process is the creation of and maintaining optimal vacuum conditions inside a growth chamber. A typical growth chamber setup looks as below:

The typical process steps are the following:?

1. Layout diamond seed/substrate
2. Close chamber and evacuate chamber for conditioning, heat up substrate
3. Introduce hydrogen
4. Turn on microwaves and generate plasma (~4000 °C) above the substrate
5. Introduce process gases and start epitaxial growth

• Methane – carbon source
• Ethanol, Acetone, or Oxygen (optional) – helps improve the quality through oxygen plasma etching effect
• Nitrogen (optional) – helps speed up the process (learned from experience and made MPCVD growing feasible economically)

6. 1 to 4 weeks of growth period

Which are the vacuum pump requirements for the growth period?

1. Initial pump down to about 2E-2 mbar base pressure
2. Maintain pressure (100-300 mbar, typically in a range of 100-130 mbar) while process gasses flow
3. Low-pressure cleanup of diamond color after production

Questions or need application support

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