Relationship between purity and dew point of semiconductor gases

Analysis of the relationship between gas purity and dew point in semiconductor manufacturing

in the field of semiconductor manufacturing, gas purity and dew point are the core parameters that affect product quality, process stability and equipment life. The two are directly related to the water vapor content and together constitute a key indicator of environmental control in semiconductor production. The following four aspects of definition, relevance, process impact and industry standards are discussed.

Definition of 1. Core Concepts

1. gas purity
   refers to the proportion of target components (e. g. nitrogen, silane) in the gas, usually expressed in the "9N" level (e. g. 99.9999999%). Semiconductor manufacturing requires a gas purity of 5N-6N, and the impurity content needs to be controlled within the range of ppb (one part per billion) or even ppt (one part per trillion).

2. dew point
   the temperature at which water vapor in a gas begins to condense into liquid water. The lower the dew point, the higher the gas dryness. For example, a gas with a dew point of -70°C contains only 1/1000 of the water content of a gas with a dew point of -40°C.

Correlation between 2. gas purity and dew point

1. water vapor as a major pollutant
   water vapor is one of the most critical impurities in semiconductor processing. Even trace amounts of moisture (ppb levels) can cause:
   • wafer oxidation: In lithography, etching and other links, moisture reacts with the silicon substrate to generate silicon dioxide, destroying the circuit structure.
   • film defect: In chemical vapor deposition (CVD), moisture causes a decrease in film uniformity and an increase in leakage current.
2. Quantitative relationship between purity and dew point
   high purity gases are necessarily accompanied by extremely low dew points. For example:
   • 6N grade nitrogen (99.9999%) requires dew point ≤-60 ℃, and corresponding water vapor content ≤ 0.1ppm.
   • Special gases (such as silane) need dew point ≤-90 ℃ to ensure molecular level process accuracy.

Effect of 3. Dew Point on Semiconductor Process

1. humidity Control of Key Process Links
   • lithography process: The photoresist expands after moisture absorption, resulting in a decrease in pattern resolution. Environmental dew point shall be controlled ≤-60 ℃ to avoid photoresist failure.
   • etching process: Excessive water content of fluorine-based gas will reduce the selectivity of etching rate, resulting in excessive sidewall roughness.
   • thin film deposition: Water introduces impurity elements (such as oxygen), changes the dielectric constant of the film, and affects the performance of the device.
2. Equipment operation and maintenance costs
   • vacuum system efficiency: High dew point gas increases the load of the vacuum pump, causing the pumping speed to drop by more than 30%.
   • Equipment corrosion: Water vapor reacts with metal parts to generate oxides, shortening the life of the equipment.

4. industry standards and control requirements

1. semiconductor Association International (SEMI) Standards
   • general gas: dew point ≤-40 ℃, suitable for machining, pneumatic tools and other scenarios.
   • Special gas: dew point ≤-70 ℃, to meet the chip manufacturing, lithography and other high-precision requirements.
   • Ultra-pure gas: dew point ≤-100 ℃, used for advanced processes below 7nm.
2. Dew Point Monitoring and Control Technology
   • online monitoring: Using a capacitive dew point meter (such as Pura Advanced Online 2), real-time measurement of dew point as low as -120 ℃.
   • Drying equipment: Through adsorption dryer (pressure dew point ≤-70 ℃) or membrane separation technology to ensure gas dryness.
   • System Design: The gas pipeline adopts 316L stainless steel electro-polished tube, and the inner wall roughness is ≤ 0.4 μm to reduce moisture adsorption.

5. Case Study: Nitrogen Supply System

take the largest amount of nitrogen in semiconductor manufacturing as an example:

• purity requirements: 99.9999 (6N grade), impurity content ≤ 1ppb.
• dew point control: Pressure dew point ≤-60 ℃, corresponding water vapor content ≤ 0.1ppm.
• System Configuration:
  • front-end filtration: remove particulate matter (≥ 0.01 μm).
  • Adsorption drying: molecular sieve adsorption of moisture.
  • Online monitoring: dew point sensor real-time feedback data to ensure the quality of gas supply.

Conclusion

gas purity and dew point are two inseparable indicators in semiconductor manufacturing. High-purity gases achieve moisture control with a very low dew point to ensure process accuracy, equipment stability and product yield. As the process node advances to 3nm and below, gas purity and dew point control will face more severe challenges, requiring continuous optimization of purification technology, monitoring systems and supply chain management to support continuous innovation in the semiconductor industry.