Abstract
Reflectance anisotropy spectroscopy (RAS) equipment is applied to monitor dry-etch processes (here specifically reactive ion etching (RIE)) of monocrystalline multilayered III–V semiconductors in situ. The related accuracy of etch depth control is better than 16 nm. Comparison with results of secondary ion mass spectrometry (SIMS) reveals a deviation of only about 4 nm in optimal cases. To illustrate the applicability of the reported method in every day settings for the first time the highly etch depth sensitive lithographic process to form a film lens on the waveguide ridge of a broad area laser (BAL) is presented. This example elucidates the benefits of the method in semiconductor device fabrication and also suggests how to fulfill design requirements for the sample in order to make RAS control possible.
Highlights
Reflectance anisotropy/difference spectroscopy (RAS/RDS) [1,2,3,4,5] is an established powerful method to monitor the epitaxial growth of monocrystalline semiconductor layers in situ [6,7] – for instance for molecular beam epitaxy (MBE)
During the process each semiconductor layer with its specific material composition can be identified by its characteristic region of the Reflectance anisotropy spectroscopy (RAS) color plot
Using the recorded reflectometric and interferometric data, represented for example by the average reflected intensity over time, in situ etch depth control of multilayered samples can be performed with accuracies better than 16 nm
Summary
Reflectance anisotropy/difference spectroscopy (RAS/RDS) [1,2,3,4,5] is an established powerful method to monitor the epitaxial growth of monocrystalline semiconductor layers in situ [6,7] – for instance for molecular beam epitaxy (MBE). There are various approaches to monitor and control the etch depth during dry-etching: With methods based on gas-phase analysis such as mass spectrometry of the residual gas [12] or optical gas-phase analysis such as optical emission spectroscopy [13,14] it is possible to achieve an end-point control [11,13,15] In this case information on the actual etch depth can only be retrieved in connection with changes in material composition at the interfaces between any two layers. An undesired deviation of the film lens layer thickness of only a few tens of nanometers may change the effective refractive index of the lens for the fundamental laser mode and the focal length of the lens, to which the lasers’ length is adapted, drastically This fabrication procedure serves as an example for all processes, where no additional etch stop layer can be incorporated. The example deals with the wafer layout necessary for RAS dry-etch monitoring
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