Using chemical vapor deposition to produce lab-grown diamonds

Using chemical vapor deposition to produce lab-grown diamonds

The diamond industry represents a unique economic case study on how scarcity impacts price: in addition to jewelry, diamonds have a variety of industrial applications due to their chemical composition and tensile strength. For many years, large diamond companies have been able to artificially stabilize diamond prices by controlling the supply of mined diamonds. However, diamonds manufactured using chemical vapor deposition have recently disrupted the industry.

High prices and high demand have spurred a growing market for lab-grown diamond manufacturing

Lab-grown diamonds are manufactured at a rate faster than every before. This shift has made the gem more accessible, and has grown even faster as our understanding of the humanitarian and environmental costs of mining naturally-occurring diamonds has grown.

Lab-grown diamonds are made using chemical vapor deposition

The Asia-Pacific region has long been the epicenter of lab-grown diamond production. India and China both manufacture diamonds, but each for different purposes: India tends to use lab-grown diamonds as high-quality gems for the fashion industry, while China uses lab-grown diamonds and diamond coatings for industrial purposes. Today, manufacturing occurs in countries around the world, and the market has become a global venture.

Improvements in CVD and manufacturing produce better diamonds

With consistent and quality-controlled manufacturing practices, lab-grown diamonds are identical to those which form naturally. This type of diamond manufacturing is done using two processes: high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) are the two processes used to manufacture diamonds.

HPHT mimics the Earth’s natural process of creating diamonds. Extremely high heat and pressure (about 2000°C  and over 1.5 million PSI) are used to simulate what would traditionally happens deep underground.

Diamonds made using CVD are a newer development. This process imitates how diamonds are formed in interstellar gas clouds. The diamond is here formed layer by layer as energy breaks the chemical bonds in gases. Both methods can yield high-grade diamonds, but CVD has become the preferred approach for several reasons.

Firstly, most CVD processes require comparatively lower temperatures and pressures than those required by HPHT, making it a simpler manufacturing process. The diamonds themselves are also chemically pure, because gases like nitrogen and boron, which are needed for HPHT and infiltrate the diamond, are not needed during the CVD process. But perhaps most importantly, CVD can be used for diamond deposition on substrates other than diamond.

This has resulted in technological advancements for many industries like optics, computer sciences, and tool production. While the biggest challenge thus far to manufacturing diamonds via CVD is the inability to yield diamonds over 3.2 carats, this is irrelevant for many industries outside of jewelry.

How CVD forms diamonds

CVD requires a process seed to act as the foundation for chemical deposition. The seed may be a thin slice of diamond or a graphite source, which is placed in a chamber that is evacuated down to a high vacuum (about 20 millitorr) to prevent contamination. Specific gases fill the chamber: generally a carbon-rich gases such as methane, and either hydrogen or oxygen. Once the chamber is filled with the gases, energy is applied to break the chemical bonds of the gases and build up the diamond atom by atom and layer by layer.

To create the energy needed for the CVD process, the gases are heated or ionized plasma is created

If the gases are heated, it is done via thermal or chemical activation. To thermally heat gases, a filament within the vacuum chamber is used to reach a target temperature between 2000-2500 °C. Less commonly, a torch is used to exothermically convert the process gases to heat the chamber to between 500-1000 °C.

Most commonly, ionized plasma is created via electrical or electromagnetic activation, using either microwaves or lasers. However, there are a variety of techniques which can be employed to make the plasma into the jet streams or balls that are used for the coating process.

Regardless of the means by which the energy is created, diamond manufacturers must carefully regulate the temperature, pressure, and gas composition that is present in their vacuum chambers during the CVD process. Changes or fluctuations in any of these three variables will impact the growth rate of the diamond, as well as its purity and color. The diagrams below demonstrate the balance of gas composition and the pressure/temperature ratio that is needed for diamonds to grow.

Triangle showing growth regions for synthetic diamonds based on the balance between carbon, hydrogen, and oxygen

Carbon/hydrogen/oxygen balance required for diamonds to grow

Triangle showing the impact of different hydrogen, carbon, and oxygen ratios on the necessary pressure and temperature conditions to make lab-grown diamonds using CVD

Impact of pressure and temperature on carbon solubility

Alicat devices used in diamond manufacturing

Alicat IVC-series pressure controller with integrated vacuum sensor

Alicat IVC-Series pressure controller

Vacuum pressure controllers ensure that pressures within the vacuum chambers are stable and accurate, to maintain the delicate balance of conditions required for diamonds to grow.

A team of Alicat vacuum applications engineers have worked with diamond manufacturers to design instruments specifically made for the pressure regulation requirements of a CVD system. The IVC-Series, an innovative upstream vacuum controller, resulted from those partnerships.

Advantages of the IVC-Series

Historically, downstream pressure control has been used for chemical vapor deposition. In a downstream system, a large throttle valve is used in combination with a separate control module to manage high volumetric flow rates. The upstream vacuum controller Alicat offers instead uses a fast-acting proportional valve that enables faster system response and better stability.

IVC-Series vacuum controller controlling gas flows into an vacuum chamber

IVC-Series pressure controller used in vacuum control for diamond manufacturing

There are many challenges manufacturers face when attempting to produce consistently high quality lab-grown diamonds. System stability, vacuum leaks, and component costs must each be carefully monitored. Alicat has addressed system stability with quality specifications: the IVC-series boasts a 1000:1 turndown ratio and an accuracy rating of ±0.5% of full scale. When these specifications are coupled with Alicat’s control algorithm, it provides flexible and accurate pressure control with an extremely fast, 2 ms sensor response time.

To tackle leaks, all Alicat devices designed for use with vacuum systems undergo helium leak tests (to 1 × 109 atm-cc/sec)to reduce risk. Finally, in respect to cost, Alicat has designed an all-in-one instrument that doesn’t need downstream throttle valves or separate control modules.

As the lab-grown diamond industry grows, Alicat is ready to help manufacturers develop the CVD systems necessary for diamond manufacturing. If you have questions, please contact one of our expert application engineers today so we can find the solution you need.