Plasma charge injection technology and its application to c-Si solar cells for field-effect passivation

Abstract

A plasma charge injection technology applicable for field-effect passivation in crystalline silicon solar cells is discussed. The technology uses an inert-gas plasma (helium, argon, N2, etc.) as a charge source and a DC bias to extract desired charges from a remote plasma source. A charging model is proposed, and it gives a good guideline to determine a proper charging operation condition for a desired injection charge density. The technology can introduce electric charges into a nitride–oxide or oxide–nitride–oxide passivation stack in a few hundred milliseconds with a charge density equivalent to or higher than that of Al2O3 in a range of 5 × 1012 to 8 × 1012 cm−2. Most-like charge injection mechanisms are discussed for both negative and positive charging. This technology uses a cheap inert-gas plasma which does not cause any parasitic film deposition nor any corrosion inside the chamber during the charging operation and, thus, does not require regular maintenance for chamber cleaning, which leads to a very low cost of ownership. This charging technology is promising for a low-cost alternative to the complex Al2O3 technology. This plasma charge injection can be another important application of the plasma technology among other well-known applications such as dry etching, thin-film deposition, sputtering, etc.