Molecular Dynamics Simulation Of Dielectric Properties Of Benzocyclobutene-Based Materials

The development of chips is an important driving force for the progress of today’s era,and large-scale integrated circuits are an important component of chips.In order to further improve the performance of large-scale integrated circuits,it is necessary to use low dielectric constant materials,so low dielectric materials have received widespread attention from researchers.Benzocyclobutene(BCB)resin materials,due to their low dielectric constant and good thermodynamic properties,are expected to be used in chips and as important interlayer dielectric materials.In the past few decades,researchers have reported a great deal on the experimental results of exploring BCB resins with low dielectric materials,and some of the results have been successfully commercialized.However,there are few reports on the research of BCB resin in simulation calculations,especially on its dielectric properties,which to some extent hinders the development of BCB resin.Therefore,this thesis uses Materials Studio(MS)software to construct a molecular model of BCB resin after cross-linking using the method of all atom molecular dynamics(MD)simulation,and systematically studies the relationship between the molecular structure and dielectric properties of BCB resin.In addition,the thermodynamic properties of BCB resin were simulated.The main research contents are as follows:(1).Molecular models of three polymers were established using MS software,namely poly(4-vinyl BCB-co styrene)(PVBS),poly(BCB monosubstituted divinylbenzene),and poly(BCB monosubstituted divinylbenzene co styrene).In the process of building molecular models of PVBS and poly(BCB monosubstituted divinylbenzene co styrene),it is necessary to adjust the proportion of repeating units in the molecular chain according to different needs,increasing from 20% to 80% in turn.The molecular weights of the three polymers are appropriately adjusted based on different systems,with each increase of 10 repeating units.Before cross-linking,use the Fortite module of MS software to optimize the structure and kinetic relaxation of the polymer molecular model to minimize its energy.The crosslinking of polymers containing BCB groups can be achieved through scripts,in which the degree of crosslinking can be set.The molecular model volume after crosslinking is compared with that before crosslinking,and the results show that the volume of the resin shrinks as the degree of crosslinking increases,and the final volume shrinkage also conforms to the actual theoretical result,which is not greater than 20%.(2).Based on(1),molecular dynamics simulations of cross-linked molecular models are conducted for a long time under different ensemble conditions.Since MS cannot directly calculate the dielectric constant of the system under study,it is necessary to import the trajectory file generated by molecular dynamics simulation into the calculation script to obtain the required dielectric constant.The simulation results show that when the degree of crosslinking,the proportion of repeating units in the molecular chain,and the molecular weight of the polymer increase respectively,the dielectric constant of the cured resin will also increase(most of the dielectric constants are between 2.45-2.70),which is relatively close to the experimental data measured within the error range(the dielectric constant is between 2.50-2.70).However,the influence of polymer molecular weight on the dielectric constant of cured resin is smaller than that of crosslinking degree and the proportion of repeating units in the molecular chain.When BCB resin undergoes curing and cross-linking,the increase in cross-linking density leads to a decrease in the bending or moving ability of the polymer main chain of the resin,and a decrease in the free volume of the resin,resulting in an increase in the dielectric constant of the resin.At the same time,it is consistent with the conclusion that cross-linking can cause volume shrinkage.(3).Thermodynamic properties are also very important for BCB resins,and having good thermodynamic properties can make them more widely used in practical applications.Based on(2),import the trajectory file into the calculation script to obtain the relationship between the density and temperature of the resin molecular model.The data points in the high and low temperature regions are linearly fitted,and the temperature corresponding to the intersection of the two fitting lines obtained is the glass transition temperature(Tg)of the system.At the maximum crosslinking degree,the Tg of the three BCB resins is quite close,ranging from 670 K to 685 K.Only the PVBS system has experimental testing data that is within a range(greater than 623K),and Tg also increases with the increase in crosslinking density.In order to verify the accuracy of Tg simulation for two other BCB resin systems,the relationship between free volume and interaction energy and temperature was measured.After fitting,a value similar to Tg can also be obtained.