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Datasheet Flow controllers for lab-grown diamonds A140
Application Note

Flow controllers for lab-grown diamonds

with chemical vapor deposition technology (CVD)

Good reliability and reproducibility are the main features for Bronkhorst mass flow controllers and pressure controllers that are used in the manufacturing of synthetic, lab-grown diamonds using chemical vapor deposition. After all, a single batch to grow these shiny gems will take as long as 300 to 600 hours, and during this entire period the process conditions need to be the same to obtain a consistent good quality of the diamonds.

Check out the Bronkhorst solution
Flow controllers in lab-grown diamonds manufacturing

Traditionally, diamonds were formed deep down below our feet in the earth’s mantle. Millions of years at high temperature and extreme pressure allowed the carbon atoms present there to be densified into the characteristic diamond crystal structure. Volcanic eruptions swept them to the earth's surface, ready to be mined. Quite a journey for these precious gems ...

In recent decades, natural diamonds have been given synthetic counterparts - even grown from the vapor phase. Synthetic lab-grown diamonds which are manufactured using microwave plasma chemical vapor deposition (CVD) technology are gaining traction. Mainly as jewelry, but also for industrial cutting and polishing purposes due to their extremely good materials properties, and in the future for semiconductor wafers. 

India is a front runner in this matter, and Bronkhorst has cooperated for many years with leading machine and system building players in the field by supplying mass flow controllers and pressure controllers for growing high-quality CVD diamonds.   

Requirements for lab-grown diamond production

To manufacture lab-grown diamonds, gaseous reactants such as methane and hydrogen are fed to a low-pressure reactor. Microwave radiation converts these gases into reactive compounds (a plasma) that deposit onto tiny diamond seed crystals present in the reactor chamber. The deposit follows the structure of the seed crystal, thereby forming a larger diamond, layer by layer. This process typically takes 300 to 600 hours – quite some time, but very much shorter than in the case of natural diamonds. After cutting and polishing, these lab-grown diamonds have the same physical, chemical and optical properties as natural diamonds.

For the batch CVD process, a constant, very low pressure (high vacuum) is required. Moreover, the gaseous reactants need to be supplied to the reactor with the same constant flow throughout the entire process.

Important topics

  • Good reliability and reproducibility of mass flow controllers and pressure controllers
  • Consistent good quality of diamonds over a long period during manufacturing
  • Understanding of the CVD process

Process solution

Bronkhorst EL-PRESS digital electronic back pressure controllers are applied to ensure the required constant value of the low pressure inside the plasma chamber. 

The EL-FLOW Select thermal mass flow controllers are used for the accurate control of the flow of gases supplied to the reactor. Methane (CH4) is used as carbon precursor, and also hydrogen (H2) is supplied to the reactor to facilitate the diamond formation. Depending on the customer, additional gases such as nitrogen (N2), argon (Ar) and oxygen (O2) can be supplied. Typical flows are in the low flow regime for hydrogen (about 1000 ml/min), and in the low to ultra-low flow regime for methane and other gases. Bronkhorst devices accurately control the flow even at ultra-low setpoints in the range of 3 ml/min and lower.

Thermal flow controller for lab-grown diamond production
Option 1: EL-FLOW Select & EL-PRESS models

By visiting relevant system building companies worldwide and understanding their needs, Bronkhorst was able to supply several solutions to obtain leak-free accurate flow control and stable pressure control to ensure high-quality diamonds. Depending on the client, various combinations of separate (1 or 2) EL-PRESS pressure controllers and (3 to 5) EL-FLOW Select thermal mass flow controllers are supplied. Bronkhorst can offer various communication protocols, such as Modbus (on 9-pin D-Sub connector for cost-effectiveness), Flowbus or Profibus.

An advantage in this low-pressure application is that all these proven devices inherently perform their control operation without any significant leakage, to enable stable and accurate process conditions. Their fast response time and low settling time support these control tasks. 

FLOW-SMS for lab-grown diamond production
Option 2: FLOW SMS module

As an economical solution, and to respond to client’s needs with respect to space efficiency, a FLOW-SMS setup is provided. These compact Surface Mount Sub-systems combine mass flow or pressure sensor modules with (control) valves or other functional accessories mounted on a rail system, based on clients’ specifications. In addition, MANI-FLOW series provide the same economical client-specific setup, but now mounted on a compact manifold. 

As a company operating worldwide, Bronkhorst has (after) sales and service support in various countries, so that any help for CVD diamond system builders is close at hand. Combined with understanding the CVD process and the needs of the market, this makes Bronkhorst a reliable partner to provide the client with a real solution.

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Multi-channel flow controller for lab-grown diamond production
Option 3: Multi-channel Flow Controllers

Bronkhorst High-Tech designs and manufactures innovative instruments and subsystems for low-flow measurement and control for use in laboratories, machinery and industry. Driven by a strong sense of sustainability and with many years of experience, we offer an extensive range of (mass) flow meters and controllers for gases and liquids, based on thermal, Coriolis and ultrasonic measuring principles. Our global sales and service network provides local support in more than 40 countries. Discover Bronkhorst®!