| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS2-ThM |
| Session: | Plasma Processing of Challenging Materials |
| Presenter: | Christopher Ahles, University of California, San Diego |
| Authors: | C.F. Ahles, University of California, San Diego A.C. Kummel, University of California, San Diego |
| Correspondent: | Click to Email |
As CMOS technology is scaled down to <10nm, new MOSFET architectures are required in order to maintain control over the device. The optimal design for such a device is the gate-all-around (GAA) architecture. Whereas in previous CMOS generations the MOSFETs were planar structures, GAA structures require highly selective isotropic etching for device fabrication. Previous isotropic gas phase selective etching of silicon employed sulfur passivation of Ge which can dope silicon, corrode process equipment, and cause ion mobility in dielectrics. In this report a sulfur-free isotropic selective etch is reported which has essentially infinite Si/Ge etch rate ratio (ERR) using in a downstream plasma. The etch rates of Si and Ge were simultaneously measured in-situ using a reactor chamber equipped with dual quartz crystal microbalances (QCMs). The gold-coated quartz crystals were sputter-coated with Si and Ge. After in-situ removal of the surface oxides with a downstream NF3/H2 plasma, the Si and Ge films were dosed with gas from a downstream plasma of H2, CF4 and Ar. It was found that a high Si/Ge ERR can be obtained over a wide range of H2/CF4 gas flow ratios, QCM temperatures, chamber pressure and plasma power. For the optimal process window, there is an etch rate >1nm/min for Si and deposition of carbon onto Ge. The nature of the passivation layer is being investigated via XPS as well as isotopic labeling in conjuction with secondary ion mass spectrometry (SIMS) studies. It is hypothesized that the high selectivity occurs due to the occupied Ge d-orbitals backbonding with an unsaturated carbon ligand, such as a CF2 carbene. This backbonding promotes the polymerization of a carbonaceous film on the Ge surface and thereby passivates the Ge against etching. Since Si does not possess occupied d-orbitals it is unable to promote the polymerization of a passivation layer as efficiently as Ge.