Paper PS2-ThA5
Capillary Jet Injection of SiH₄ in the HDP-PECVD of SiO₂: What We Can Learn from It

Thursday, October 23, 2008, 3:20 pm, Room 306

This paper reports on the deposition of silicon dioxide films from a silane/oxygen gas mixture in a matrix distributed ECR PECVD system. In order to investigate the influence of the primary silane flux and the precursor consumption on the deposition rate and material properties, undiluted silane is first injected into the system through a gas ring positioned around the periphery of the substrate holder, at a distance of 3 cm. The same set of depositions is then done using a 1 mm diameter capillary tube located 3 cm vertically above the substrate surface. The microwave power, pressure, substrate bias and silane gas flow are varied. The material properties are studied using spectroscopic ellipsometry, FTIR spectroscopy and transmission measurements. The plasma is characterized using optical emission spectroscopy (OES) and differentially pumped quadrupole mass spectrometry (QMS). The maximal deposition rate when using a 16 sccm SiH4 and 40 sccm O2 gas mixture is found to increase from 1 nm/s up to 2.16 nm/s when the gas ring is replaced with the capillary jet injection system. This increase is attributed to the large increase in the primary flux of undissociated silane onto the substrate surface. Using an intentionally inhomogeneous deposition resulting from the capillary jet injection and studying the thickness normalized OH absorption in the deposited film at various distances from the capillary injection point, we gain insight into the contribution of the partial pressure of water (which is the main by-product of the reaction between silane and oxygen) on the OH content in the silicon oxide. It is observed that the silicon oxide deposited directly below the capillary injection point has an integrated OH absorption band intensity which is approximately half that of a point 3 cm away from it. Reducing the distance between the injection point and the substrate also leads to a narrowing of the OH absorption band, where the associated vibration mode at 3350 cm-1 practically disappears and only the isolated Si-OH vibration bonds at 3650 cm-1 are retained. By looking at the films thickness at various distances from the capillary jet, it is seen that the primary, beam-like SiH4 is the largest contributor to the deposition rate when using a capillary jet. A Direct Simulation Monte Carlo (DSMC) technique is used to model the flux of the precursor gases onto the substrate plane. The simulation results are compared with the experimental findings.