DC sputtering Vs RF sputtering : Difference between rf and dc sputtering

Sputtering is a widely used thin-film deposition technique in industries like electronics, optics and materials science. Among the various sputtering methods, DC (Direct Current) and RF (Radio Frequency) sputtering stand out for their distinct working principles and applications. While DC sputtering is often employed for conductive materials, RF sputtering offers versatility with both conductive and insulating materials. This article dives into the core difference between RF and DC sputtering, highlighting their working principles, advantages, limitations and typical use cases.

What is Sputtering:
Sputtering is highly versatile vacuum coating system which is used for deposition of various coating materials.

Sputtering

Plasma gas is used ti knock atoms out of the target. As a result, atoms gets deposited on wafers as shown. Higher pressure generates better coverage. The excess energy of metal ions helps to increase surface mobility (i.e. movement of atoms on surface).

DC sputtering

DC Sputtering

• In DC sputtering, source of power is DC (Direct Current) type.
• DC power is usually preferred for electrically conductive target materials as it is easy to control DC power.
• chamber pressure is usually 1 to 100 mTorr
• It is chaper technique when large quantities of large substrates are dealt with.
•  In this technique, positively charged sputtering gas is accelerated towards the target. This results in ejection of atoms which gets deposited on substrate.

RF sputtering

RF Sputtering

• In RF sputtering, source of power is AC (Alternating Current). Instead of DC voltage to cathode, RF at about 13.5 MHz is being applied.
• RF peak to peak voltage is 1000 V, electron densities are 109 to 1011 Cm-3 and chamber pressure is 0.5 to 10 mTorr
• RF power is suitable for all the materials but most commonly used for depositing films from dielectric target materials.
• Deposition rate is low compare to DC sputtering.
• It is used for smaller substrate sizes due to high cost factor of RF power supplies.
• The RF sputtering consists of two processes. In the first cycle, target material is negatively charged. This causes polarization of atoms. The sputtering gas atoms are attracted towards source where they knock out source atoms. Here source atoms and ionized gas ions remain at target surface due to polarization of target.
• In the second cycle, target is positively charged. This causes ejection of gas ions and source atoms due to reverse polarization. These are accelerated toward substrate and hence deposition will occur.

Difference between rf and dc sputtering

Following table summarizes core differences between RF and DC sputtering techniques.

Features DC Sputtering RF Sputtering
Sputtering type Magnetron only Magnetron or diode
Target materials Conductive only All the targets
Power Source Uses a direct current (DC) power source. Uses a radio frequency (RF) power source, typically 13.56 MHz.
Material Suitability Suitable only for conductive materials. Suitable for both conductive and insulating materials.
Target Charging Cannot sputter insulating targets due to target charging. Prevents target charging through alternating RF electric fields.
Complexity Simple setup and operation. More complex setup due to the RF power source and matching network.
Cost Lower equipment cost. Higher equipment cost due to RF generators.
Deposition Rate Generally higher deposition rates for conductive materials. Deposition rates are often lower than DC sputtering.
Applications Commonly used for metal films and conductive coatings. Ideal for dielectric, insulating, and mixed-material films.
Plasma Generation Relies on a steady plasma for material removal. Alternating RF fields sustain a stable plasma even with insulating materials.
Maintenance Easier maintenance due to simpler components. Requires more frequent tuning and complex maintenance.
Efficiency Higher efficiency with conductive materials. Lower efficiency but more versatile material handling.
Sputtering rate 100% of DC 20% of DC, no magnetron
Compaign length (i.e. loss of anode) Good Excellent

Conclusion

Both DC and RF sputtering are essential thin-film deposition techniques, each suited to specific material requirements and applications. DC sputtering excels in simplicity and efficiency for conductive materials, while RF sputtering’s versatility makes it ideal for a wider range of materials, including insulators. Understanding these differences ensures the right method is chosen for a given application, optimizing performance and quality.


What is Difference between



RF and Wireless Terminologies