Plasma Modification Of Si-O-Si Bond Structure in Porous Sioch Films
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1079-N07-03
PLASMA MODIFICATION OF Si-O-Si BOND STRUCTURE IN POROUS SiOCH FILMS Fedor N Dultsev1, Adam M Urbanowicz2,3, and Mikhail R Baklanov2 1 ISP SB RAN, Lavrentiev ave., 13, Novosibirsk, 630090, Russian Federation 2 AMPS, IMEC, Kapeldreef 75, Leuven, 3001, Belgium 3 Department of Chemistry, Katholieke Universiteit Leuven, Leuven, 3001, Belgium ABSTRACT Plasma modification of SiOCH low-k films is analyzed by means of Molecular Mechanics. It is shown that the most probable mechanism of SiOCH modification in He plasma is removal of hydrogen atoms from CH3 groups. The change of Si–O–Si bond angles depends on the amount of the formed –СН2* (СНх) groups. During the followed exposure in NH3 plasma, NH2* radicals bind СНх groups with Si forming a –CH2– Si–O–Si–O–Si–O–Si– chain. The end of this chain gets bound to its beginning through NH2. This process is the reason of pore sealing. INTRODUCTION Porous SiOCH low-k films with carbon containing hydrophobic groups are the most favored class of materials for advanced interconnect technology. Although the matrix of these materials has properties similar to SiO2, their chemical stability and reactivity strongly depend on porosity, pore size and their interconnectivity. The use of porous materials brings challenges related to the structural properties such as percolation phenomena. In addition to changes in mechanical properties (Young's modulus), porous materials exhibit high chemical activity, which brings complications to their application and technological processing. The exposure of these films to a plasma leads to the loss of hydrophobic groups and to the densification of their silica backbone. Both effects cause an unwanted increase in the dielectric constant, as well as an increase in the leakage current. The extent of this damage depends on the plasma conditions such as chemistry and power and on the porosity of the film. On the other hand, treatment in certain plasmas [1, 2] may cause pore sealing, which results in a decrease in the chemical activity of these layers. Changing an inert gas and excluding the ion component in treating the surface the authors demonstrated that the film reactivity is affected by the UV radiation of the plasma. For instance, it was shown in [3, 4] that the treatment of SiO2 films in He plasma caused an increase in the rate of etching these layers in 1% HF solution. Another observation is that sequent exposure of SiOCH low-k film in He and NH3 plasma results in complete sealing and passivation of the film surface [1] . The effect of porosity on chemical activity can be considered in two aspects: first, due to the developed surface, with the reaction proceeding not at the boundary but over the whole volume: we will call this effect macrostructural; second, due to changes in the electron structure of surface atoms, which leads to changes in the chemical properties of surface atoms: to be called microstructural effect. It is the investigation into the microstructural effect that will allow us to understand how we can change the properties of
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