Electronics

In the semiconductor (electronic chip) industry, anhydrous ammonia (NH3) is a mission-critical "electronic specialty gas" (ESG). It is primarily used as a source of nitrogen atoms for creating insulating layers and crystalline structures on silicon wafers.

The following details the specific applications, chemical processes, and purity requirements.

1. Deposition of Silicon Nitride Layers

The most significant use of anhydrous ammonia is in Chemical Vapor Deposition (CVD). It is reacted with silicon-bearing gases to deposit thin films of Silicon Nitride (Si3N4).

• The Function: Silicon nitride is a hard, dense material used as an electrical insulator, a passivation layer (protective coating), or a "mask" to block oxidation in specific areas of the chip.5
  
  

• The Reaction: Inside a high-temperature furnace or plasma chamber, ammonia reacts with silane (SiH4) or dichlorosilane (SiH2Cl2).
  
  

• Reaction Example:
  3SiH4 + 4NH3 --> Heat Si3N4 + 12H2

• Why Ammonia? It provides a high-purity, reactive source of nitrogen that can be precisely controlled to ensure the film is uniform at the atomic level.
  
  

2. Manufacturing LEDs and Power Chips (MOCVD)

Ammonia is the essential feedstock for creating Compound Semiconductors, specifically Gallium Nitride (GaN). This is the material used for blue/white LEDs (like those in phone screens and lightbulbs) and high-power chips for EV chargers.

• The Process: In a process called Metal-Organic Chemical Vapor Deposition (MOCVD), ammonia is flowed over a heated wafer along with gallium sources (like Trimethylgallium).
  
  

• The Growth: The ammonia "cracks" (breaks apart) at high temperatures, releasing nitrogen atoms that bond with the gallium to grow the crystalline GaN layers necessary for light emission.

3. Semiconductor Cleaning (SC-1 Process)

While "anhydrous" refers to water-free ammonia gas, chip fabs often mix this gas with ultra-pure water and hydrogen peroxide on-site to create Ammonium Hydroxide (NH4OH).

• Standard Clean 1 (SC-1): This mixture is widely used in the "RCA Cleaning" process to wash silicon wafers.

• Role: The ammonia solution is alkaline (high pH), which helps electrically repel particles from the wafer surface, effectively removing dust and organic contaminants before new circuit layers are added.

4. Purity Requirements: "Electronic Grade"

The ammonia used in agriculture (fertilizer) is roughly 99.5% pure. This would instantly destroy a semiconductor chip. The chip industry uses Electronic Grade Ammonia, which must be 99.999% (5N) to 99.9999% (6N) pure.

Impurity Type/Danger to Chip

Moisture (H2O)

Causes uncontrolled oxidation on the wafer surface.

Metals (Fe, Na)

Even a few atoms can short-circuit transistors or alter electrical conductivity.

Particulates

A microscopic dust particle acts like a boulder, blocking circuit patterns.

Summary of Uses

• Si3N4 Insulation: Acting as the nitrogen donor for insulating films in logic and memory chips.

• GaN Growth: Growing the active layers for LEDs and high-power radio frequency (RF) chips.

• Wafer Cleaning: Mixed with water to remove particles from wafers between manufacturing steps.