Chemical Repair of plasma damaged porous ultra Iow-κ SiOCH film using a vapor phase process

摘要

Ultra 1ow-κ dielectrics (ULK) face a lot of difficulties especially with respect to plasma processing after patterning of such layers [1], The requirement of a κ-value of smaller than 2.5 [2] is achieved by the introduction of carbon and porosity into SiO~2 layers. It is reported that during plasma processes the ULK film is damaged, which is related to the carbon loss [3]. This is explained due to smaller dissociation energy for Si-C (~ 447 kJ/mol) compared to Si-0 (~ 800 kJ/mol) [4]. It was observed that during the carbon depletion dangling bonds occur [5], which form new Si-0 or Si-OH bonds after exposing to atmosphere or during the plasma process. Hence, an unfavorable degradation of the dielectric properties occurs, i.e. increasing κ-value [6]. For ULK layer restoration, silylation based repair processes are proposed [7]. During the repair process mainly Si-OH bonds are replaced by less polar tri-, di- or monomethylsilyl groups, using e.g. super critical CO_2 [8,9], vapor phase [10,11] or spin on processes. Many factors can influence the silylation reaction, like amount of reactive groups, kind of reactive groups and steric hindrance [7] of the silylation agent. Due to steric hindrance, chemicals with one reactive group like hexamethyldisilazane are not satisfactory. Those chemicals do not react with all existing silanol groups, since one trimethylsilyl group can blocks neighboring silanol groups [11]. Chemicals with two or three reactive groups tend to