No abstract

Germanium and Germanium-On-Insulator (GeOI) MOSFETs with high-k gate dielectrics have received recent attention for the advanced technology nodes, because of the better carrier transport properties in Ge compared to Si. For Ge or GeOI CMOS, it is mandatory to determine Ge dedicated resist stripping processes, because of the Germanium non-compatibility with actual cleaning solutions. An initial compatibility study shows a passivation effect on germanium during dry step for high N2/ (O2+N2) plasma ratio. For the post active area etching, dry stripping performed on patterned Poly-Ge-On-Insulator (PolyGeOI) wafers shows good compatibility. The lateral Ge consumption due to the water rinse step is minimized by dry process, indicating a plasma passivation effect. Post implant stripping is especially difficult because the Si typical solutions are highly aggressive for Ge, and also because of the resist graphitization. Using a ramping temperature process, a good resist removal efficiency has been achieved.

Due to the downscaling of devices, the HF vapor release process, one of the most effective techniques for MEMS release, becomes more challenging regarding stiction. An initial compatibility study shows that many metals are compatible except for Ni and Cu. A design of experiment was performed on thermal oxide wafers to obtain the parameters for a stiction free process. Nevertheless, current MEMS release processes can not be used on NEMS structures due to a more aggressive shape factor. The solution to adapt current HF vapor MEMS release process to NEMS consists of reducing of the etchrate, reducing the water layer on the surface during the etch step and thereby stiction occurrence. For very challenging structures, reducing the etch rate is not sufficient to avoid stiction and heating process has to then be used.The evolution from Micro Electro Mechanical Systems (MEMS) to Nano Electro Mechanical Systems (NEMS) technology, due to CMOS co-integration requirement and performances enhancement, requires a drastic decrease of device characteristic dimensions (from 10 µm to 100 nm). Hence, release process becomes more and more critical in regards with stiction, stiffness and material compatibility issues. HF vapor is known to be an effective technique for the microstructure dry release, limiting the presence of water on surface (1) and, subsequently, avoiding stiction. The aim of this study is to find a free adhesion process with an acceptable compatibility level to be used on NEMS structures. ExperimentalProcesses were performed in a batch HF vapor etch tool manufactured by Semitool Inc. A simplified flow diagram of the system is shown in figure 1. The system operates at ambient pressure and uses a patented (2) HF/alcohol vapor process. Vapors are generated from liquid sources using an inert carrier gas flowing through a patented (3) vapor generator. There are three gas lines: one for each generator (HF and IPA) and one to keep the total flow constant for etch rate uniformity. Mass Flow Controllers (MFCs) allow calibrating proportions of HF and IPA vapors in the etchant vapour mix. In the following, HF or IPA ratios are given in total flow percentage.The etchant vapor is delivered to a high density polyethylene (HDPE) chamber which can accommodate wafer sizes up to 200mm in diameter and load sizes from 1 to 25