Cure is a significant process during back end of the line fabrication of integrated circuits with hydrogen silsesquioxane since it affects structure and properties of the spin on dielectric material. Reported herein is the effect of soak temperature, time, and oxygen concentration process parameters on structure and properties of hydrogen silsesquioxane. Results of the study emphasize the importance of an inert environment during the baseline recommended cure conditions of 400 °C for one hour in order to avoid oxidation and formation of polar silanol or water species. A 350 °C cure temperature is more robust to oxidation providing similar or improved properties. Shorter cure times result in similar structure and properties as the baseline cure which suggests that lower temperature and/or shorter cure time may provide value worth investigating by integrated circuit manufacturers.

A study of the growth of a-SiC:H films by plasma-enhanced chemical vapor deposition (PECVD) from two organosilicon precursors, silacyclobutane (H2CH2SiCH2CH2 or SCB) and methylsilane (CH3SiH3), is described. A capacitively coupled, parallel plate PECVD system was used to grow films at 250 °C and deposition pressure of 2.0 Torr. Standard (13.56 MHz) and low frequency (0.125 MHz) rf sources were used to generate the deposition plasma. Depositions were performed with and without argon dilution (neat) of the precursor. We report some of the first process/property relationships for organosilicon based a-SiC:H films grown using a fixed, controlled set of deposition conditions. Included are data on film composition, structure, dielectric constant and stress. Films deposited from silacyclobutane had much higher carbon concentrations than those deposited from methylsilane, but in both cases the carbon fraction in the film was lower than that in the precursor. It is found that the plasma drive frequency has a stronger influence on film composition than argon dilution of the precursor during deposition. The low frequency plasma significantly increases the film growth rate for the neat precursor process. Depending on the growth process, the relative dielectric constants of the a-SiC:H films ranged from 3.6 to 8.7. The variation of the dielectric constant over the frequency range 0.1–1000 kHz was negligible. All measured film stress was compressive and ranged from 0.1 to 1.0 GPa depending on precursor and plasma frequency. Films deposited from a 10% organosilicon/90% argon mixture showed higher dielectric constants, higher refractive indices and less bound hydrogen when compared to neat organosilicon precursor depositions. The films exhibited excellent oxidation resistance and could not be etched in 6:1 buffered HF solutions. The properties of the a-SiC:H films are compared to PECVD hydrogenated silicon nitride and discussed in the context of applications requiring low temperature deposited protective dielectric coatings.

Thin film properties of hydrogen silsesquioxane (HSQ) cured at different temperature under N2 and H2/N2 ambients have been studied. In this study, it was found that compared to an N2 ambient, film curing in an H2/N2 ambient will impact HSQ properties when the temperature is 400°C – 500°C. H2/N2 ambient can be used to minimize the dielectric constant while increasing modulus of the films. The data indicates that H2 can minimize the oxidation of the HSQ films and maintain the dielectric properties.

Atomic structure impacts on the dielectric and mechanical properties of hydrogen-silsesquioxane (HSQ) were investigated to determine the sensitivity of HSQ to Si-H bond degradation during thermal processing. It was demonstrated that the dielectric properties of HSQ films are not sensitive to Si-H bond degradation up to 50 % if polar silanol or water species are not induced during thermal processing at a temperature of ≤ 450 °C. However, as the Si-H bond density is reduced, the mechanical properties are changed due to the increasingly formed Si-O-Si networks. This provides an opportunity for tuning mechanical properties per application requirements by process optimization.

CF4 plasma etching of hydrogen-silsesquioxane films on bare silicon substrates was conducted. An increase in average etching rate and a decrease in dielectric constant from 2.9 to 2.7 were observed after a top layer was removed from the surface of the film, indicating that a negative density depth gradient in the film was developed during the cure processing, A small part of the reduction in dielectric constant may be attributed to structural change resulting from the plasma interaction with the films since a small amount of Si-F bonds were identified in the surface layer of the film after plasma etching. There are indications in the x-ray photoelectron spectroscopy (XPS) spectra that traces of fluorocarbon polymer residue have been generated during the plasma etching. The results of this study also indicate a possibility of obtaining a lower dielectric constant HSQ film by plasma etching.