AVS 54th International Symposium | |
Plasma Science and Technology | Wednesday Sessions |
Session PS1+NS-WeM |
Session: | Plasmas in Nanotechnology |
Presenter: | S. Borel, CEA-Leti MINATEC, France |
Authors: | S. Borel, CEA-Leti MINATEC, France C. Arvet, STMicroelectronics D. Watanabe, Shibaura Mechatronics Corporation, Japan |
Correspondent: | Click to Email |
The selective removal of a SiGe sacrificial layer is a key step in the realization of several architectures that are based on the SON technology. Such a process has been developed and studied in 200mm, showing very good results in terms of selectivity by using CF4 as an etching gas. This competence has been transferred in 300mm by using a new generation chemical dry etching tool that offers an additional and alternative source of fluorine which consists in NF3. A process based on this environment-friendly molecule has been developed and compared with the CF4 reference in terms of SiGe:Si selectivity while keeping a comparable etch rate. In that aim, a strong dilution (1:10) was necessary because of the high dissociation level of NF3 that results in high etch rates. Morphological analyses clearly show that the selectivity obtained by using NF3 is prohibitive for the realization of advanced devices. Indeed, the selectivity value is around 3, which means that the thinning of the Si cap is only 3 times lower than the SiGe tunnel depth whereas it needs to be higher than 30 (it reaches 70 by using CF4). Surface analyses by XPS reveal that a Si substrate exposed to the CF4 process presents some carbon, which suggests a passivation mechanism that may be involved in the selectivity. With the carbon-free NF3 molecule, this phenomenon does not occur, hence the lack of selectivity we observe. As a conclusion, even if it is possible to etch SiGe faster than Si by using NF3, the reference process made of CF4 remains the best solution for the tunnel etching of advanced devices where a controlled etch rate is necessary and a high SiGe:Si selectivity is mandatory.