基于X射线衍射的GaN薄膜厚度的精确测量

Thickness measurement of GaN films by X-ray diffraction

结合Williamson-Hall plot方法和线型分析方法的优点,提出了一种有效分离有限晶粒尺寸和非均匀应力等X射线衍射展宽效应的方法,可以用于GaN外延层厚度等参数的快速精确测量.用该方法对一系列在蓝宝石衬底上生长的厚度在0.7—4.2μm的GaN外延膜进行了测量,并与椭圆偏振光谱法测量结果进行了比较,结果表明其差别<4%,反应了这种方法的准确性.

Precise measurement and control of GaN-film thickness is very important for GaN-based material epitaxy and device fabrication.However,GaN-films heteroepitaxially grown on large-mismatch substrates,such as sapphire,SiC and Si,etc.,usually show a mosaic structure,which causes great difficulty to the GaN-film thickness measurement.Combining the advantages of Williamson-Hall plot method and diffraction profile shape analysis method,a new strategy was presented to effectively distinguish the X-ray diffraction broadening factors of finite crystallite size and inhomogeneous strain,which can be used to precisely and reliably determine the thickness of epitaxial films.The thickness of a series of GaN films grown on sapphire substrates in the range of 0.7—4.2 μm were measured by this method.Comparing with the thickness obtained from spectroscopic ellipsometry measurements,the difference was found to be within 4%,which shows the excellent performance of this method.