Epitaxial Ge-Gd2O3 on Si(111) substrate by sputtering for germanium-on-insulator applications

Germanium-on-insulator (GeOI) technology is a potential-alternative to the bulk-silicon based devices for radio-frequency (RF), and complementary metal oxide semiconductor applications at advanced technology nodes. A thin germanium channel is the key enabler of high mobility transistors and group-IV photonic devices. A prohibitive cost of GeOI wafers may discourage high volume manufacturing (HVM) despite promising performance. Here, we demonstrate epitaxial Gd 2 O 3 -Ge-Gd 2 O 3 thin film growth on Si(111) substrate in an HVM platform - RF magnetron sputter system, where, the first Gd 2 O 3 layer acts as buried-oxide (BOX) in the GeOI wafer. The second Gd 2 O 3 layer is used as a cap-layer to be removed later using wet etching. Both the Gd 2 O 3 layer is grown epitaxially at 750 ∘ C , while the germanium layer is grown at room temperature and crystallised later by solid phase epitaxy (SPE) technique. The entire growth is performed without vacuum-break, to enable high throughput and excellent interface control. To compare the quality of the heterostructure, this sputter based SPE is performed on: (1) in-situ sputter grown, versus (2) ex-situ molecular-beam-epitaxy (MBE) grown epitaxial Gd 2 O 3 BOX layer. The x-ray diffraction analysis confirms the formation of twin-free epitaxial Ge layer in the case of in-situ sputtered Gd 2 O 3 while twinned Ge layer is observed in the case of ex-situ MBE grown Gd 2 O 3 . The twinning of the Ge layer in the ex-situ process is further supported by transmission electron microscopy analysis. Finally, we have performed an experiment to study the impact of Gd 2 O 3 BOX layer thickness on the crystal quality of Ge layer and show that the Ge layer crystal quality remains intact irrespective of BOX layer thickness. Therefore, we have achieved twin free Ge epitaxy in RF magnetron sputter system, equivalent to in-situ All-MBE SPE process. Such a process enables low-cost GeOI wafer manufacturing for cost-effective RF transistors.