Working principle of vacuum coating CVD electric furnace

The working principle of vacuum coating CVD (chemical vapor deposition) electric furnace is based on chemical vapor deposition technology, combined with vacuum environment and high-temperature heating system, to form a uniform and dense thin film on the substrate surface through chemical reaction. The following is a detailed analysis of its working principle:

1. Core working principle
Establishment of vacuum environment
Purpose: To eliminate impurities such as oxygen and water vapor from the air, and to prevent them from participating in reactions or contaminating the film; Simultaneously reducing the collision frequency of gas molecules, making it easier for the reactive gas to reach the surface of the substrate.
Implementation method: The reaction chamber is evacuated to a high vacuum state (usually 10 ⁻³~10 ⁻⁶ Pa) through vacuum equipment such as mechanical pumps and molecular pumps to ensure the purity of the reaction environment.
Introduction and control of reactive gases
Gas selection: According to the coating requirements, introduce gases containing target elements (such as SiH ₄, NH ∝, CH ₄, etc.) and carrier gases (such as Ar, N ₂).
Flow control: Accurately adjust the gas flow rate through a mass flow meter (MFC) to ensure that the reaction gases are mixed in a stoichiometric ratio and maintain a stable reaction rate.
High temperature heating and chemical reactions
Heating system: using resistance heating (such as tungsten wire, graphite heater) or induction heating to heat the reaction chamber to the target temperature (usually 300-1200 ℃).
Chemical reaction: At high temperatures, reaction gas molecules decompose or activate, generating active atoms, ions, or free radicals. These active species undergo chemical reactions on the surface of the substrate, forming a solid thin film.
Thin film growth and control
Growth mode: Thin film growth follows island growth, layered growth, or mixed growth modes, which are influenced by factors such as substrate temperature, gas pressure, and reaction time.
Thickness control: By adjusting reaction time, gas flow rate, and temperature, the film thickness can be precisely controlled (from nanometer to micrometer level).

2. Key components and functions
vacuum system
Mechanical pump: rough vacuum is applied to reduce the pressure in the reaction chamber to 10 ⁻¹~10 ⁻ ² Pa.
Molecular pump: High vacuum pump, further reducing the pressure to 10 ⁻³~10 ⁻⁴ Pa.
Vacuum gauge: Real time monitoring of reaction chamber pressure to ensure stable vacuum degree.
heating system
Heating element: such as tungsten wire, graphite heater or induction coil, providing a uniform high-temperature environment.
Temperature control system: Temperature is monitored through thermocouples or infrared thermometers, and precise temperature control (± 1 ℃) is achieved by combining PID controllers.
gas supply system
Gas source: high-purity gas cylinder or gas generator.
Pipeline: Stainless steel or quartz pipeline to avoid gas pollution.
Valves and flow meters: Control gas on/off and flow rate to ensure that reaction gases are mixed in proportion.
Reaction chamber
Material: Usually made of quartz or stainless steel, high temperature resistant and chemically inert.
Substrate holder: Fix the substrate and adjust its position to ensure uniform deposition of the film.

3. Process flow
Loading and vacuuming: Place the substrate into the reaction chamber, close the furnace door and start the vacuum pump to achieve the target vacuum degree.
Heating and preheating: Start the heating system to heat the reaction chamber to the set temperature, while introducing a carrier gas (such as Ar) to eliminate residual gases.
Reaction gas introduction: Introduce the reaction gas according to the stoichiometric ratio to begin thin film deposition.
Growth control: By adjusting temperature, gas flow rate, and reaction time, the thickness and properties of the film can be controlled.
Cooling and wafer removal: After deposition is complete, stop heating and introduce inert gas to cool the reaction chamber. After the temperature drops to a safe range, remove the substrate.

4. Application Fields
Vacuum coated CVD electric furnaces are widely used in:
Semiconductor industry: Deposition of insulating layers such as Si ∝ N ₄ and SiO ₂, or diamond films for heat dissipation.
Optical components: preparation of anti reflective films, reflective films, or filters.
Tool coating: Deposition of hard coatings such as TiN and TiC on the surface of the tool to improve wear resistance.
New energy field: Deposition of transparent conductive oxide (TCO) thin films for solar cells.