Doped or Quantum-Dot Layers as In Situ Etch-Stop Indicators for III/V Semiconductor Reactive Ion Etching (RIE) Using Reflectance Anisotropy Spectroscopy (RAS)

Abstract

Reflectance anisotropy spectroscopy (RAS), which was originally invented to monitor epitaxial growth, can—as we have previously shown—also be used to monitor the reactive ion etching of III/V semiconductor samples in situ and in real time, as long as the etching rate is not too high and the abrasion at the etch front is not totally chaotic. Moreover, we have proven that—using RAS equipment and optical Fabry‒Perot oscillations due to the ever-shrinking thickness of the uppermost etched layer—the in situ etch-depth resolution can be as good as ±0.8 nm, employing a Vernier-scale type measurement and evaluation procedure. Nominally, this amounts to ±1.3 lattice constants in our exemplary material system, AlGaAsSb, on a GaAs or GaSb substrate. In this contribution, we show that resolutions of about ±5.6 nm can be reliably achieved without a Vernier scale protocol by employing thin doped layers or sharp interfaces between differently doped layers or quantum-dot (QD) layers as etch-stop indicators. These indicator layers can either be added to the device layer design on purpose or be part of it incidentally due to the functionality of the device. For typical etch rates in the range of 0.7 to 1.3 nm/s (that is, about 40 to 80 nm/min), the RAS spectrum will show a distinct change even for very thin indicator layers, which allows for the precise termination of the etch run.

The interfacial structure of InP(100) in contact with HCl and H2SO4 studied by reflection anisotropy spectroscopy

“…4,34–36 Furthermore, RAS is also employed to control layer-by-layer etching of multilayered semiconductors. 37…”

“…4,[34][35][36] Furthermore, RAS is also employed to control layer-by-layer etching of multilayered semiconductors. 37 For RAS, linearly polarised light impinges at near-normal incidence on the surface. The difference in the reectivity, Dr, with respect to two orthogonal directions in the surface plane (x, y) is detected by analysis of the polarisation as a function of the photon energy, scaled with the overall reectivity, r:…”

In Situ and Real-Time Monitoring of Doping Levels by Reflectance Anisotropy Spectroscopy (RAS) during Molecular Beam Epitaxial (MBE) Growth of III/V Semiconductors

“…In [14], Lastras-Martinez et al have already discussed the use of RAS for the in situ determination of doping levels in both n-and p-type GaAs. In [15,16], our group has pointed out that doping levels can be retrieved via RAS even during reactive ion etching (RIE) instead of growth.…”

Reactive Ion Etching (RIE) Induced Surface Roughness Precisely Monitored In-Situ and in Real Time by Reflectance Anisotropy Spectroscopy (RAS) in Combination with Principle Component Analysis (PCA)

“…Te RAS equipment can also be used to determine the current etch depth with very high precision on the order of a couple of lattice constants [8,9]. In this case, the Fabry-Perot oscillations of the genuine RAS signal spectra or of the average refectivity spectra are used.…”