Influence of Additive N₂ on O₂ Plasma Ashing Process in Inductively Coupled Plasma

Area of Science:

• Materials Science
• Plasma Physics
• Semiconductor Manufacturing

Background:

• Oxygen plasma ashing, crucial for semiconductor cleaning, often uses nitrogen (N2) to enhance the ashing rate.
• The ashing rate is typically correlated with oxygen radical concentration, measured by Optical Emission Spectroscopy (OES).

Purpose of the Study:

• To investigate the relationship between N2/O2 mixing ratios, RF power, and ashing rates in oxygen plasma.
• To identify discrepancies between OES measurements and actual ashing rates.
• To propose a method for accurately determining optimal ashing conditions.

Main Methods:

• Comprehensive experimental study of O2 plasma ashing with varying N2/O2 ratios and RF powers.
• Plasma diagnostics including Optical Emission Spectroscopy (OES), Langmuir probe, and cutoff probe.

Main Results:

• Observed that oxygen radical density measured by OES does not always accurately predict the ashing rate.
• Demonstrated that electron density is a critical plasma parameter influencing the ashing rate.
• Identified conditions for achieving the maximum ashing rate.

Conclusions:

• Relying solely on OES for oxygen radical concentration is insufficient for optimizing ashing processes.
• Incorporating electron density measurements alongside OES and other plasma diagnostics provides a more accurate method for inferring maximum ashing rates.
• This approach can enhance the efficiency and precision of next-generation semiconductor plasma processes.