Which Plasma Parameters Need Measuring?

1. The four core parameters of test plasma

1. Electron density ne (unit: cm⁻³)

It determines the 'strength of activity' of plasma.

• Form of expression: throughprobe Current ChangeThen reverse engineer the electron density;

• Meaning: Insufficient density leads to low etching/cleaning efficiency; large density fluctuations result in unstable chip yield.

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2. Electron temperature Te (unit: eV)

It determines the 'level of activation' of plasma.

• Form of expression: Fit the electron temperature through the **voltage-current characteristic curve (I-V curve)**;

• Significance: If the temperature is too high, it will damage the material; if it is too low, the reaction will be insufficient. It needs to be strictly controlled within the 2–10 eV range.

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3. Ion Energy / Ion Flux

Determines the directionality of etching and the density of the film.

• Forms of expression: Ion energy is reflected in the probe bias voltage; flux is calculated through the ion saturation current;

• Meaning: Excessive energy can erode the substrate, and unstable flux can lead to uneven film thickness.

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4. Active particle concentration (free radical concentration)

Elements such as F, Cl, O, OH, etc., determine the efficiency of chemical reactions.

• Forms of expression: Often indirectly judged through spectral intensity, but can also be associated with probe current and voltage signals;

• Meaning: If there are not enough particles, etching/cleaning is insufficient; if there are too many, it can easily cause damage.

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2. Why is the test ultimately presented in the form of 'current and voltage'?

Because of the test probe of plasmaHeadEssentially, it is an electrical measurement sensor, which, after being inserted into plasma, will produce:

• Voltage (Potential Distribution)

• Current (electron/ion collection current)

By collecting the I-V curve and then using the plasma physical model, parameters such as electron density, electron temperature, and ion energy can be calculated.

So in industry testing, the plasma parameter is derived from the current/voltage signal.

3. The Real Difficulty of Test plasma

1. plasma Strong electromagnetic interference in the environment

Radio frequency plasma sources (13.56MHz or higher frequencies) can interfere with measurement signals, causing:

• Current waveform distortion;

• Voltage signal drifts;

• The data jitter is severe.

  The difficulty lies in how to achieve high anti-interference and high signal-to-noise ratio.

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2. ExploreHeadInsertion will cause disturbance plasma

exploreHeadIt is made of metal, and after entering the cavity, it will change the local discharge state.

The difficulty lies in:

• Make the disturbance as small as possible;

• Find a balance between 'measurable' and 'non-disruptive'.

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3. Low-temperature plasma parameter changes rapidly and fluctuates greatly

Electron density and temperature respond instantaneously to changes in power, pressure, and gas flow, resulting in:

• Transient features are difficult to capture;

• High requirements for data real-time performance.

4. There are large differences in the parameter ranges of different materials and different processes

Different processes in semiconductors have completely different parameter requirements, for example:

• Etching: high electron density, control ion energy;

• Deposition: moderate electron temperature, stable flux;

• Cleaning: Sufficient active particles.

  The difficulty lies in establishing a universal and customizable testing plan.

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5. high-precision measurement is difficult with calibration

plasmaThe parameter spans a large range (10¹⁰~10¹³ cm⁻³), probeHeadRequired:

• High sensitivity;

• Wide range;

• Repeatability;

• Long-term stability.

  The difficulty lies in ensuring that probe is long-term reliable and consistently produced in large quantities in an industrial environment.

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4. Conclusion

• plasma Parameters must be measured, otherwise the process cannot be accurately controlled.

• These parameters are ultimately quantitatively measured through **current and voltage signals (I-V curves)**;

• measurement challenges lies in: electromagnetic interference, plasma disturbance, large parameter fluctuations, significant differences in different processes, and difficulty in guaranteeing measurements accuracy.

Professional plasma discharge testing probe was created precisely to address these pain points, turning plasma from 'invisible' into 'quantifiable, monitorable, and optimizable'.