In-situ etch depth control with precision around 1 nm via reflectance anisotropy spectroscopy during reactive ion etching of monocrystalline III/V semiconductors
Experimental Condensed Matter Physics
Final Report Abstract
In semiconductor technology layers have to be thinned by etching with very high pre- cision. This is usually done with the help of ionized gases (plasmas) with chemical etch component. The notion is “reactive ion etching“ (RIE). Oftentimes the achieved etch depths are measured after the etching outside the RIE plasma chamber. Thus possible irregularities of the etch process may only be noticed afterwards and may identify the complete sample load as wastage. But reflectance anisotropy spectroscopy (RAS) equipment allows for the collection of information on the activities at the etched surface during the etch process. This way the etch depth and its temporal evolution can be monitored in real-time and in-situ (without taking the sample out of the RIE plasma chamber) during the etch process. In RAS, light is impinging onto the sample and informations on the etched surface are extracted from the features of the reflected light. All etch-depth monitoring accuracies achieved in this project have been better than ±20 nm and thus by far sufficient for nearly all plasma etch applications. 20 nm make up 1/3000 of the thickness of a typical human hair or the 140-fold of the distance bet- ween any two adjacent atomic layers in the semiconductor crystals. To improve accuracy, more than one wavelength/color from the RAS light spectrum is used. This way the optical equivalent to a mechanical Vernier scale (on a Vernier caliper) is realized. During the project even five wavelengths have been used simulta- neously, i.e. one scale plus four slightly different Vernier scales for comparison. Thus, accuracies of ±0.8 nm have been achieved, equivalent to just ±5.2 distances bet- ween adjacent atomic layers in the semiconductor crystal. And RAS signal changes due to changes in material composition, which have delibe- rately been applied already during the growth of the monocrystal, can be used as in- dicators for a precise etch stop. In the project typical III/V semiconductors of optoelectronics like GaAs have been used. They are called this way, because their atoms stem from the third and the fifth group of the periodic table of chemical elements.
Publications
- Doped or quantumdot layers as in situ etch-stop indicators for III/V semiconductor reactive ion etching (RIE) using reflectance anisotropy spectroscopy. Micromachines, special issue on “Etching for Semiconductor Nanofabrication” 12 (2021) 502 (14 pages)
G. Sombrio, E. Oliveira, J. Strassner, J. Richter, Chr. Doering, H. Fouckhardt
(See online at https://doi.org/10.3390/mi12050502) - Interferometric in-situ III/V semiconductor dry-etch depth-control with ±0.8 nm best accuracy using a quadruple-Vernier-scale measurement. J. Vac. Sci. Technol. JVST-B 39, 5 (2021) 052204 (7 pages)
G. Sombrio, E. Oliveira, J. Strassner, Chr. Doering, H. Fouckhardt
(See online at https://doi.org/10.1116/6.0001209)
