AVS 45th International Symposium
    Electronic Materials and Processing Division Friday Sessions
       Session EM-FrM

Paper EM-FrM8
Reaction Pathways/Energetics for Chemical Attack of Amorphous Si-O-F and C-F-(H,OH) Low-k Dielectric Thin Films by Water Molecules

Friday, November 6, 1998, 10:40 am, Room 316

Session: Fabrication and Characterization of Semiconductor Device Layers
Presenter: H. Yang, North Carolina State University
Authors: H. Yang, North Carolina State University
G. Lucovsky, North Carolina State University
Correspondent: Click to Email
Amorphous films of Si-O-F and C-F-(H,OH) are being considered for low-k inter-metal dielectrics in advanced CMOS devices. The relative stabilities of these different types of dielectrics with respect to chemical attack by water molecules are discussed. FTIR studies have provided the basis for a pseudobinary alloy model for Si-O-F with F-atoms incorporated solely in Si-F bonds. Network bonding statistics have been used to calculate the probability for F-atoms being i) isolated¹ on Si-atoms separated by one or more O-Si-O groups, ii) paired¹ on Si-atoms connected through at most one O-atom, and iii) more strongly clustered. Ab intio calculations are used to study reaction pathways for attack of Si-F bonds by water. For isolated Si-F bonds, the energy of attachment, E@sub a@, of a water molecule through one H-bond is <0.1 eV, whereas E@sub a@ for attachment of a water molecule to a pair of Si-F bonds is ~5 times larger. The reaction between a single Si-F bond and a water molecule, HOH + Si-F --> Si-OH + HF, is exothermic by ~0.1 eV, whereas the reaction between a pair of Si-F bonds and a water molecule, HOH + 2Si-F --> 2HF + Si-O-Si, is exothermic by 0.7 eV. Based on the alloy model statistics, the ab initio calculations predict good stability against attack by water extending to ~10 at.% F, corresponding to a dielectric constant of 3.2 to 3.4. The situation is quantitatively different for the C-F materials. Reaction pathways for attack of C-F bonds by water have also been studied by the same ab initio approach. The attachment energies of water for isolated, and near-neighbor C-F bonds are each significantly lower, ~0.1 eV, and reaction pathways are endothermic: e.g., HOH + 2C-F --> 2HF + C-O-C is endothermic by 1.6 eV. This suggests that initial attack of C-F low-k materials by water must be through other bonding groups such as C-H or C-OH. Ab initio calculations are being extended to C-F-(H,OH) materials to study reaction pathways and reaction energetics. Supported by ONR, NSF and INTEL Corporation.