Charge referencing issues in XPS of insulators as evidenced in the case of Al‐Si‐N thin films

Abstract

AbstractAccurate charge referencing in XPS of insulating specimens is a delicate issue. This difficulty is illustrated in the case of Al‐Si‐N composite thin films deposited by reactive magnetron sputtering with variable composition from pure aluminum nitride to pure silicon nitride. The samples were mounted with Au‐coated metallic clamps. Argon sputter cleaning was required to remove a surface native oxide before analysis. For charge referencing implanted argon atoms from the sputter gas and a small amount of gold re‐deposited from the metallic clamps onto the specimen surface during sputter cleaning were evaluated. For the argon atoms, a surprisingly large chemical shift (∼1 eV) and a significant peak broadening (0.6 eV) of the Ar 2p3/2 photoelectron line were found with varying the Si content of the films. This could be related to chemical and structural changes of the Al‐Si‐N films. Hence implanted argon could not be used for charge referencing of Al‐Si‐N samples. In contrast to the implanted argon, the Au 4f7/2 line width of the gold re‐deposited onto the sample surface did not depend on the Si content of Al‐Si‐N films. A constant energy shift (∼1.2 eV) of the Au 4f7/2 line as compared with bulk gold was, however, found, which was related to the size of gold particles formed on the insulating films. Therefore gold could be reliably used to study chemical shifts of sample‐relevant species in Al‐Si‐N films, but the absolute binding energies of Al 2p, Si 2p and N 1s photoelectrons could not be determined. Copyright © 2011 John Wiley & Sons, Ltd.