Preparation of AlN thin films by reactive sputtering and optical emission spectroscopy during sputtering

Abstract

Aluminum Nitride (AlN) thin films were prepared by reactive rf-magnetron sputtering in a mixed gas atmosphere composing of argon and nitrogen. The deposition rate, electrical resistivity and crystal structure were studied as a function of partial pressure of nitrogen (P _N2). Total pressure(P _N2+Ar) was controlled to maintain a constant pressure of 6.0 ×10⁻² Pa. The structure of as-prepared films can be divided into three regions from X-ray diffraction analysis: (1) P _N2 ≤ 6.0 ×10⁻³ Pa, Al, (2) P _N2 = 1.2 ×10⁻² Pa ∼ 2.4 ×10⁻² Pa, a mixed phase of Al and AlN, (3) P _N2 ≥ 3.0 ×10⁻² Pa, AlN. With increase of P _N2, the deposition rate of the films decreased drastically around P _N2 = 2.4 ×10⁻² Pa, and finally approached to a constant value of 25 Å/min around P _N2 = 6.0 ×10⁻¹ Pa. This is proved from the measurement of optical emission spectroscopy to occur by the formation of nitride on the surface of aluminum target. AlN thin films deposited in higher P _N2 exhibited a higher crystallity and a higher refractive index because of less nitrogen deficiency.

Key Words:

• Reactive sputtering
• optical emission spectroscopy
• partial pressure of nitrogen
• surface state of target
• formation of nitride
• optical property