Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Area of Science:

• Materials Science
• Semiconductor Physics
• Surface Chemistry

Background:

• Ex situ phosphorus-doped polycrystalline silicon on silicon oxide (poly-Si/SiO) passivating contacts are crucial for solar cell efficiency.
• These contacts can degrade during high-temperature firing treatments (≥800 °C), impacting performance.
• Degradation is linked to processing conditions, including dielectric layers and firing temperature.

Purpose of the Study:

• Investigate the firing stability of poly-Si passivating contacts.
• Propose a mechanism for degradation involving hydrogen.
• Quantify hydrogen's role in the poly-Si/SiO interface during firing.

Main Methods:

• Secondary ion mass spectrometry (SIMS) to measure hydrogen concentration.
• Firing poly-Si/SiO structures at various temperatures.
• Annealing in nitrogen to remove hydrogen.
• Measuring recombination current density parameter (J₀).

Main Results:

• Excess hydrogen at the poly-Si/SiO interface deteriorates passivation and increases J₀.
• Firing with silicon nitride (SiN) introduced additional hydrogen, causing further degradation.
• Complete hydrogen removal via annealing fully recovered surface passivation.
• Degradation dependence on crystallite properties and doping profiles was modeled.

Conclusions:

• Hydrogen plays a dual role: beneficial in moderation, detrimental in excess.
• Excess hydrogen accumulation during firing is the primary cause of poly-Si passivation degradation.
• Controlling hydrogen diffusion and concentration is key to achieving stable, high-performance passivating contacts.