The Investigation On Preparation Of Porous Low Dielectric Silicon Based Films By Using Spin-on Deposition

Since 1920's, the feature size of ULSI (Ultra-large scale integrate circuit) is scaling down to a very small value according to the prediction of so-called"Moore's Law". In order to reduce the RC sign delay, power dissipation and cross-link noise between metal and interconnects caused by size shrinking continuously, the porous low dielectric constant (low- k) and ultra-low dielectric constant (k <2) materials recently received much close attention. In this thesis, we focus our research on the sol-gel with spin-on (compatibility with existent ULSI technology) technology to prepare low- k thin films. To the best our knowledge, we systematically studied the properties of these Silicon based films, such as preparation, microstructure, chemical bonds and leakage current density. We achieved some valuable breakthrough.1. Through sol-gel method with spin-on technology, we deposited the porous low dielectric constant MSQ (methylsilsesquioxane) thin films. We use ethanol as solvent and HCl as the catalyzer and MTMS (methyltrimethoxysilane) as the main materials to prepare MSQ colloid in room temperature. We prepared the MSQ colloid into MSQ thin films by using SOD (Spin-on Deposition). The MSQ is difficult to prepare because the property of MSQ is very lively. As one of the many methods to prepare MSQ thin films, this method possesses many virtues, such as simple equipment, easy to be controlled, convenient adulteration. We analyzed detailedly the properties of low-k MSQ thin films which prepared by using D4 (Octamethyl cyclotetrasiloxane) as sacrificial porous materials. FTIR investigated that the proper annealing temperature is 500oC. The dielectric constant of the MSQ thin films reduced to k=2.1. The leakage current density of the thin films annealed at 400oC lowered one order of magnitude comparing with no D4. 2. The effect of dielectric constant of thin films was discussed detailedly in different annealing temperature. The contribution of the highly polarized Si-OH components to the orientation polarization will increase the k value of the thin films. Furthermore, the Si-OH bonds in the HSQ (hydrogensilsesquioxane ) films lead to moisture uptake, which is responsible for the increase of k value and leakage current density. In this thesis, the Si-OH bonds of HSQ films can be weaken after being annealed in N2, which is very valuable. We introduced the structural and dielectric varieties of these HSQ films which using D4 and D5 (decamethylcyclopentasiloxane) as sacrificial porous materials respectively. FTIR investigated that (1) the HSQ films of adding D4 and no D4 both produced Si-OH bonds after being annealed in vacuum, but they were weaken after being annealed in N2. The reason of the appearance of Si-OH bonds was that Si-H and Si-O bonds both were destroyed after being annealed. The -OH bonds and C-H bonds of the sample of adding D4 both were weaken after being annealed at 400oC for 1.5 h in N2. These results investigated that water and organic matter were disappeared. It can be explained with the following expression. Si-OH +HO-Si = Si-O-Si + H2OThe properties of sample of adding D4 and no D4 were different after being annealed in different condition. The dielectric constant of sample of adding D4 is the lowest than others after being annealed at 400oC for 1.5 h in N2. The dielectric constant of sample of no D4 without any treatment is the highest. The dielectric constant of sample of adding D4 was increased after being annealed at 400oC for 1.5 h in vacuum. The reason is that the Si-OH bonds appearaned after the thin films were annealed in vacuum. The leakage current density of samples with O2 plasma treatment is higher one order magnitude than others. When E =1 MV/cm , The leakage current density of samples is 3.0038×10-8 A/cm2 with O2 plasma treatment and followed to be annealed at 350oC for 1.5 h in N2.(2) The analysis of low-k HSQ thin films with adding D5, FTIR investigated that it is benefit to Si-H bonds at higher temperature. The proper annealing condition is in N2. As we all know, Si-O cage structure is good to lower the dielectric constant. The D5 was decomposed after being annealed at 500oC for 1.5 h in N2, which resulted in porous to reduce the density of HSQ thin films. It is benefit to Si-H bonds with higher temperature. Si-CH3 (~1260 cm-1) and C-H (~2960 cm-1) were broken to form Si-OH bonds after being annealed in vacuum.We compared the dielectric constant with annealed treatment and without treatment. The dielectric constant is lower after being annealed. The dielectric constant of thin films with annealed treatment increased with the increase of annealing temperature. The leakage current density of samples was higher after being annealed at 400oC for 1.5 h in N2, The reason is that the decomposition of D5 produced many porous. The leakage current density of samples was lower after being annealed at 500oC for 1.5 h in N2. The reason is that the structure of HSQ thin films became compact and uniformity after being annealed. The intensity of Si-O-Si cage structure at 400oC is greater than 500oC and 300oC3. We first use CH4 plasma treated the HSQ films then were annealed in N2. The structural change of these films was introduced. They changed little with different CH4 plasma treatment time. (1) From the FTIR results, the CH4 plasma treatment can resist the structure of HSQ films to be destroyed after being annealing with the increase of treatment time. (2) The CH4 plasma treatment can keep the characterization (low leakage current density and low dielectric constant) of HSQ films with the increase of annealing temperature.