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Precise Control of Gas Delivery for Liquid and Solid Precursors

vapor delivery methods


In semiconductor manufacturing, transistors have evolved significantly over the years, from planar device architectures to FinFETS and now Gate-All-Around (GAA) to help support the development of various process nodes. These developments often demand novel precursors to support manufacturability. Accurate and repeatable delivery of precursors is critical to wafer performance, uniformity, and yield as the semiconductor industry embarks on leading-edge technology nodes.

Types of Transistors

Types of transistors


Three of the most common methods of liquid and solid precursor delivery are detailed below:

Bubbler System

This conventional method, which has been around since the 1970s, features a vessel that contains the precursor liquid or solid. A temperature-controlled bath maintains the precursor temperature. A carrier gas is introduced into the liquid and forms small bubbles which float to the surface, allowing the vapor to attain equilibrium vapor pressure. The resulting mixture is delivered to the process chamber.

Flow Scheme for Bubbler System
Flow scheme

System Requirements

  • Absorption rate of the precursor into the carrier gas
  • Temperature control of the precursor
  • Precise flow control of the carrier gas
  • Accurate pressure control of the head space of the precursor vessel

Gas Delivery Solution


In a bubbler system, delivery of the carrier gas into the liquid precursor is achieved by the Brooks Instrument GF100 Series mass flow controller (MFC). Designed using a flexible platform, the high-purity all-metal flow path delivers industry-leading accuracy, repeatability, and reliability. This MFC features:
  • 300 millisecond settling time
  • MultiFlo™ gas and range programmability
  • Optional pressure transient insensitivity (PTI)
  • Local display
  • SEMI F20 compliant 
  • Extremely low wetted surface area, and
  • A corrosion resistant Hastelloy® sensor tube and valve seat.

In addition, the Brooks Instrument PC100 Series pressure controller (PC) with an integral pressure sensor and high-speed control valve, provides accurate and repeatable pressure control in both upstream and downstream configurations.

Vapor Draw System

Less complex than the bubbler method, a vapor draw system features a heated vessel containing a liquid or solid precursor. Heating the precursor increases its vapor pressure to overcome the inherent pressure drop of the mass flow controller, delivering the vapor to the chamber. In many cases, vapor draw systems require high-temperature mass flow controllers, particularly with low pressure vapor materials.

Flow Scheme for Vapor Draw System
Flow scheme

System Requirements

  • Precise temperature control of the precursor to provide consistent vapor pressure
  • Accurate and repeatable control of the vapor flow
  • Heating of the mass flow controller and tubing to prevent precursor from condensing

Vapor Delivery Solution

The Brooks Instrument GF120XHT High Temperature mass flow controller is suitable for precise flow control of precursor vapors at temperatures up to 150°C. This platform features a high temperature flow sensor/control valve module and remote electronics. An optional heater jacket with an integral temperature controller is also available.

Direct Liquid Injection (DLI) System

More complex than the bubbler and vapor draw approaches, a DLI system can deliver higher vapor flow rates. With this method, the liquid is supplied to an atomizer, breaking it down into fine mist-like droplets before entering the vaporizer. A carrier gas provides energy to assist in the vaporization of the precursor.

Flow Scheme for Direct Liquid Injection System
Flow scheme

System Requirements

  • Precise temperature control of the vaporizer
  • Accurate and repeatable liquid flow control into the vaporizer
  • Accurate and repeatable flow control of the carrier gas into the vaporizer
  • Heating of tubing downstream of vaporizer to prevent condensation

Liquid & Gas Delivery Solution

The Brooks Instrument Quantim liquid mass flow controller  is suitable for accurate and repeatable liquid flow control into the vaporizer. Utilizing a Coriolis flow sensor; the Quantim measures liquid mass flow directly independent of fluid properties. In addition to direct control of mass flow rate, the Quantim provides secondary outputs for density and temperature. 

To achieve accurate and repeatable flow control of the carrier gas into the vaporizer, the Brooks Instrument GF100 Series mass flow controller is a suitable selection. Once again, the flexible platform it's built upon utilizes a high purity all-metal flow path that delivers industry-leading accuracy, repeatability, and reliability.


The Bubbler System, Vapor Draw System, and Direct Liquid Injection System are the three most common methods of liquid and solid precursor delivery. All three systems have different approaches but all require industry-leading accurate, repeatable mass flow control and pressure control solutions from Brooks Instrument.

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