Covalent Grafting of PMMA Organic Film on Porous Silicon for Achieving Ultralow-k Organic Films

In the current electronics industry, chip interconnect density is continuously increasing and high-frequency communication is further developed. To effectively reduce the adverse effects such as resistance–capacitance delay and signal crosstalk, it is urgent to develop organic dielectric films with lower dielectric constants. In this study, chemical grafting method via aryl diazonium chemistry is used to deposit polymethylmethacrylate (PMMA) films on the porous Si surface. The differences in surface morphology and structure of thin films on flat silicon and porous silicon are studied. In addition, we study the effect of substrate porosity on the dielectric constant, and finally obtain porous PMMA films with dielectric constants ranging from 1.9 to 1.5. Compared with the PMMA film prepared on flat silicon, the film prepared on porous silicon has the advantages of faster growth rate, larger thickness adjustable range, stronger adhesion to the substrate, and lower dielectric constant. The dielectric constant of uniform porous PMMA films obtained in this experiment is further decreased compared with inorganic SiO2 (ε1 = 3.9) and dense PMMA films (ε1 = 2.8–2.4). And the dielectric loss of PMMA films also decreases with the increase of porosity. This is a method for preparing porous polymers, which is more suitable for in situ thin film preparation in high-density electronic interconnections than traditional methods for preparing porous polymers. Theoretically, this method can be used to prepare other vinyl organic films on porous silicon surface, making it have better application prospects in the field of higher-frequency communication in the future.