| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuM |
| Session: | Plasma Surface Interactions I |
| Presenter: | Nobuyuki Kuboi, Sony Corporation, Japan |
| Authors: | N. Kuboi, Sony Corporation, Japan T. Tatsumi, Sony Corporation, Japan T. Kinoshita, Sony Corporation, Japan T. Shigetoshi, Sony Corporation, Japan M. Fukasawa, Sony Corporation, Japan J. Komachi, Sony Corporation, Japan H. Ansai, Sony Corporation, Japan |
| Correspondent: | Click to Email |
Silicon nitride (SiN) is as essential as silicon (Si) and silicon oxide (SiO2) for fabricating complementary metal oxide semiconductor (CMOS) devices. Damage on Si substrates is caused during etching of the transistor side-wall and the contact through the drain region [1], and this can greatly affect transistor properties. Hence, for CMOS devices to achieve high performance, it is important to control the etching process quantitatively along with the mechanism of the SiN surface reaction.
We propose a surface reaction model for the SiN etching process by fluorocarbon (C4F8/O2/Ar) and hydrofluorocarbon (CH2F2/O2/Ar) plasma based on the Slab model of SiO2 [2]. The surface layer is assumed to consist of two layers: a reactive layer divided by several thin slabs and a deposited C-F polymer layer on the reactive layer. We considered physical and chemical reactions in detail including reactivity of radicals (C, F, O, and H), dangling bonds ratio, outflux of N, and generation of by-products (HCN, C2N2, CH, CF2, SiF2, and SiF4) as ion assist, which depend on process parameters. We confirmed that absolute values and trends of SiN etch rate, polymer thickness, damage thickness, and selectivity of SiN/SiO2 and SiN/Si along with gas flow rates of C4F8 and CH2F2 were consistent with experimental data of conductively coupled plasma.
Furthermore, to analyze 3D damage distribution affected by the etched profile, we developed a new 3D simulation technique using an extended voxel model (called “smart voxel”) also including the above Slab model. By using gas fluxes with local pattern effect, the Slab model is solved at each voxel. Then, the etch rate and thicknesses of polymer and damage are derived. Smart voxel has details of the history of the etching situation and gives them around existing voxels when etch front is evolved in the next calculation time step. By repeating these procedures, 3D damage distribution considering a time-dependent etched profile can be realized. In addition to this new concept, modeling of gas transportation in the pattern treated as fluid is adopted without interaction between voxels, which is different from a Monte Carlo (MC) method. Hereby, 3D damage for multi-layer (Si/SiN/SiO2) can be predicted much faster and more accurately than the conventional MC model in spite of a large scale micro-meter. We will show a 3D etched profile and damage distribution for SiN side-wall etching and discuss how to control etching parameters to achieve low damage.
Acknowledgements: We thank Prof. S. Hamaguchi for stimulating discussion.
[1] K. Katahira et al. J. Vac Sci. Technol. A27, (2009) 844.
[2] N. Kuboi et al. Jpn. J. Appl. 50, (2011) 116501.