| AVS 65th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS-TuP |
| Session: | Plasma Science and Technology Division Poster Session |
| Presenter: | J. Leon Shohet, University of Wisconsin-Madison |
| Authors: | J.L. Shohet, University of Wisconsin-Madison S.-H. Kim, University of Wisconsin-Madison H.M. Nguyen, University of Wisconsin-Madison P. Xue, University of Wisconsin-Madison J. Blatz, University of Wisconsin-Madison H. Cheng, University of Wisconsin-Madison Y.-H. Lin, NSRRC, Taiwan J.-F. de Marneffe, IMEC, Belgium M. Redzheb, IMEC, Belgium S. Armini, IMEC, Belgium C.-C. Chen, NSRRC, Taiwan Y. Wu, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
VUV exposure of dielectrics during processing can cause damage and can also be beneficial.. The goal of this work is to optimize the “beneficial” spectrum of photon radiation during plasma processing. To fully separate the effects of charged-particle bombardment a synchrotron can be used to provide a continuous spectrum of radiation over the range that most processing plasmas generate. In this work, four low-k samples were provided by IMEC. Their properties before exposure are as follows:
| Precursor | Template | UV cure | k value at 100 kHz | |
| Sample 1 | PMO | CTAC (C) | No | 2.35 |
| Sample 2 | MSQ | BrijL4 (L4) | No | 2.36 |
| Sample 3 | MSQ | BrijS10 (S10) | No | 2.26 |
| Sample 4 | MSQ | BrijS10 (S10) | Yes | 2.13 |
To determine the spectral effects of irradiation a five-step procedure was followed. The steps are (1) a rapid photon energy scan to measure the substrate current caused by photoemission as a function of photon energy. (2) Determine which photon energies generate the highest and lowest substrate currents. (3) Irradiate samples separately at the photon energy for the (a) the highest and (b) the lowest substrate current. (4) Measure the substrate current as a function of time for each of the monochromatic irradiations. (5) Following the monochromatic irradiation, a rapid photon energy scan was made again to determine whether changes could be observed in the dielectrics.
For each case, the substrate current begins at a high value and then decays as a function of time until it reaches a steady state. This is typically found after photoemission occurs because the dielectric acquires a net positive charge and thus photoemitted electrons tend to be attracted back to the dielectric. It should be emphasized that the substrate current does not decay to zero but reaches a constant value which is caused by photoinjection of electrons from the silicon substrate.
The damage effects were measured by examining the changes in dielectric constant, dielectric thickness, mechanical properties using nanoindentation, and chemical bond structures using FTIR. It was determined that VUV irradiation with photon energies > 7 eV increased the concentration of silicon dangling bonds in low-k SiCOH. Photons of lower energy were not able to bread the Si-O bonds that have a dissociation energy of 6.3 eV. TDDB degradation and negative mobile-charge generation were observed when the photon energy was greater than 9 eV. The k value increased when the dielectrics were exposed to photon energies > 8 eV. VUV photon irradiation increased the film hardness at photon energies of 10.2 and 11.8 eV. The dielectric constant increased slightly after exposure for all samples.