Analysis of MBE grown AI(x)Ga(1-x)As-GaAs heteroepitaxial layers by rutherford backscattering

The Rutherford Backscattering (RBS) technique has been optimized for the measurement of thin (>85Å) alternating layers of A1(x)Ga(l-x)As and GaAs, which are at the limit of resolution of standard RBS measurements. RBS analysis of these structures provides both layer thicknesses and Al content. This information is useful for device processing since the layer thicknesses impact the FET threshold voltage and the Al content is important for proper selective chemical etching. Experimental conditions for the beam energy, detection angle, and sample rotation have been determined which allow measurement of the layer thicknesses to a precision of ±20-30Å (for layers >85A) and of the Al content,x, to a precision of ±.02. Comparison of the RBS data with Transmission Electron Microscopy (TEM), Cathodoluminescence (CL), and Reflection High Energy Electron Diffraction (RHEED) measurements on the same material showed very good agreement between the different techniques. The advantage of RBS is that it can measure much thinner layers than CL and it provides thickness and composition information at the same time whereas TEM only provides thickness for this particular material. RBS is currently used tocharacterize a monitor wafer from each day’s run to provide a processing baseline for the MBE growth.