Applications of Electronic Specialty Gases in TFT-LCD Manufacturing and a Technical Analysis of Ultra-High-Purity Delivery Systems

Introduction

Thin-film transistor liquid crystal displays (TFT-LCDs) are currently the most widely used flat-panel display technology, and their manufacturing process involves complex physical and chemical processes. Specialty electronic gases (hereinafter referred to as “specialty electronic gases”) serve as core process materials in the film deposition and etching stages of TFT-LCD array fabrication; their purity, stability, and delivery safety directly determine the panel’s yield and performance. This paper begins with the TFT-LCD manufacturing process, systematically reviews the application of electronic specialty gases in each key process step, and analyzes the technical architecture of ultra-high-purity specialty gas delivery systems.

TFT-LCD is currently the most widely used flat-panel display technology (image for illustrative purposes only)

Overview of TFT-LCD Manufacturing Processes

                                TFT-LCD Process Flowchart (For Reference Only)

The manufacturing process for TFT-LCD panels can be divided into three major stages: the front-end array process (Array), the mid-end cell assembly process (Cell), and the back-end module assembly process (Module). Among these, specialty electronic gases are primarily used in the film deposition and dry etching stages of the front-end array process.

The core of the array process is to construct a multilayer structure of thin-film transistors

(TFT), including the gate metal layer, gate insulator layer (SiNx), amorphous silicon semiconductor layer

(a-Si), source and drain electrode metal layers, and the ITO pixel electrode layer. The deposition and patterning of each thin film layer rely on specific process gases.

Applications of Specialty Gases in Core Manufacturing Processes

CVD Deposition Process

Chemical vapor deposition (CVD), particularly plasma-enhanced chemical vapor deposition (PECVD), is a core process for depositing non-metallic thin films in the TFT-LCD array fabrication process. This process activates gas molecules via a plasma, causing chemical reactions to occur on the substrate surface and resulting in the deposition of solid-state thin films. The primary electronic specialty gases used in the PECVD process include:

Silane (SiH₄): Serves as a silicon source gas for depositing amorphous silicon (a-Si) semiconductor layers and silicon nitride (SiNx) insulating layers

Ammonia (NH₃): Reacts with silane to form silicon nitride films and serves as a nitrogen source

Phosphine (PH₃): Used for n-type doped amorphous silicon layers (n⁺ a-Si) to form ohmic contact layers

Nitrous oxide (N₂O): Reacts with silane to deposit silicon dioxide (SiO₂) films

Nitrogen trifluoride (NF₃): Used for plasma cleaning of the CVD chamber to remove deposits from the chamber walls

In addition, bulk gases such as high-purity hydrogen (H₂) and high-purity nitrogen (N₂) are also used in the process, serving as carrier gas, purge gas, and process atmosphere gas, respectively.

    Shenzhen Wofly Technology CVD Gas Supply Project Showcase (For Reference Only)

Sputtering Process

Magnetron sputtering falls under the category of physical vapor deposition (PVD) and is primarily used to deposit metal films such as gate electrodes, source/drain electrodes, and indium tin oxide (ITO) pixel electrodes.

The basic principle of sputtering film deposition involves bombarding the surface of a target with charged particles in a vacuum chamber, causing atoms from the target to be ejected and deposited onto the substrate. The sputtering process has specific requirements for process gases: the deposition gas must not react chemically with the target material; therefore, inert gases are the most suitable choice. In industrial production, argon (Ar) is typically used as the sputtering working gas, though helium (He) is also used in some process scenarios.

For reactive sputtering processes (such as the deposition of ITO transparent conductive films), oxygen (O₂) is introduced into the inert gas to react with the target material’s composition and form an oxide film.

Ultra-High Vacuum High-Energy Pulsed Magnetron Sputtering Coating Equipment (For Reference Only)

Etching Process

The etching process is a key step in transferring the photoresist pattern to the underlying film. The TFT-LCD array process primarily employs dry etching (plasma etching), which utilizes reactive free radicals in the plasma to chemically react with the material being etched, generating volatile byproducts that are then evacuated by a vacuum pump. Different combinations of etching gases must be selected for etching different material layers:

• Etching of non-metallic films (e.g., SiNx, a-Si): Commonly used are fluorine- or chlorine-containing gases such as sulfur hexafluoride (SF₆), carbon tetrafluoride (CF₄), and chlorine (Cl₂)
• Metal film etching (e.g., Al, Mo, Cr): Commonly used gases include chlorine (Cl₂), hydrogen chloride (HCl), and boron trichloride (BCl₃)
• ITO etching: Hydrogen-containing gases or hydrochloric acid-based mixed gases may be used

The specialty gases used in the etching process are mostly flammable, explosive, highly toxic, or highly corrosive; therefore, extremely high standards are required for the gas delivery system’Seal Integrity, safety, and exhaust gas treatment capacity.

                       Internal Structure of an Etching Chamber (For Reference Only)

Analysis of the Architecture of an Ultra-High-Purity Specialty Gas Delivery System

A complete ultra-high-purity specialty gas delivery system consists of units such as gas source storage, primary pressure regulation, purification and filtration, secondary distribution, and end-use. These units are connected via high-purity stainless steel piping to form a closed-loop, controllable gas supply system.

Cylinder Cabinet

The cylinder cabinet serves as the gas source end of a specialty gas system, used to store cylinders and perform primary pressure reduction and gas supply switching. Its core functions include:

• Securing and connecting cylinders, equipped with an automatic switching panel to enable seamless switching between primary and backup gas sources
• A primary pressure-reducing valve reduces high-pressure gas to intermediate pressure (typically 0.3–0.5 MPa)
• Negative-pressure ventilation design maintains a negative pressure inside the cabinet to prevent leaked gas from escaping
• Equipped with a gas detector to monitor gas concentrations inside the cabinet in real time; in the event of an anomaly, it triggers audible and visual alarms and automatically shuts off the gas supply

     Shenzhen wofly Technology: Various Types of Custom-Made Special Gas Equipment

Valve Box (VMB)

The Valve Manifold Box (VMB) is a secondary distribution unit in specialty gas delivery systems. Located between the specialty gas room and the process equipment in the cleanroom, it is often referred to as the “last mile” of specialty gas delivery. Its primary functions are:

• To distribute a single gas source into multiple branches, each supplying different process equipment
• Each branch is equipped with an independent diaphragm valve, pressure reducer, and pressure sensor to enable independent control
• The enclosed enclosure design, equipped with an exhaust port, is suitable for hazardous gases such as SiH₄, NH₃, and Cl₂
• Supports independent purging and maintenance of individual branches without affecting normal gas supply to other branches

             Shenzhen wofly Technology Gas Conveyance Projects (For Reference Only)

Purifier

Purifiers are installed at the gas source or upstream of the point of use to thoroughly remove impurities from the gas. Common purification technologies include:

• Catalytic deoxygenation: Using a catalyst to cause impurity oxygen to react with hydrogen to form water, which is then removed by an adsorbent
• Molecular sieve adsorption: Removes polar impurities such as water vapor and carbon dioxide through physical adsorption
• Getter purification: Uses gas-absorbing agents such as zirconium-aluminum alloys to adsorb reactive impurities at high temperatures
• Membrane separation: Separates impurities by exploiting differences in gas permeation rates

Purifiers configured for high-end processes can elevate gas purity to 7N or higher, controlling impurity levels to the ppb or even ppt range.

        Shenzhen wofly Technology Purification System Engineering (For Reference Only)

Gas Detectors and Safety Interlocks

Gas detectors are deployed in special gas rooms, VMB installation areas, and around process equipment. They utilize detection principles such as electrochemical, infrared absorption, or semiconductor technologies to perform real-time online monitoring of target gases. The system is linked to the central control room (GSM); when a gas leak is detected, it automatically executes the following interlock actions:

• Trigger audible and visual alarms
• Automatically shut off the gas supply valve for the corresponding gas line
• Activate the emergency exhaust system
• Upload alarm information to the central monitoring system

               Shenzhen Wofly Technology Alarm System Projects (For Reference Only)

Exhaust Treatment System

Exhaust gases emitted from process equipment contain unreacted specialty gases and reaction byproducts, and must be treated by an exhaust gas treatment system (scrubber) to meet regulatory standards before being discharged. Common treatment methods include:

• Wet Scrubber: Uses a sprayed chemical solution to absorb and neutralize acidic or alkaline gases
• Plasma Scrubber: Decomposes toxic and harmful gases using high-temperature plasma
• Combustion Scrubber: Oxidizes and decomposes flammable gases at high temperatures

Shenzhen Wofly Technology Water-Washed Exhaust Gas Treatment Equipment (For Reference Only)