| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Friday Sessions |
| Session PS2-FrM |
| Session: | Plasma Surface Interactions II |
| Presenter: | Shuichi Ogawa, Tohoku University, Japan |
| Authors: | A. Saijian, Tohoku University, Japan Y. Kotanikawa, Tohoku University, Japan Y. Ohtomo, Tohoku University, Japan S. Ogawa, Tohoku University, Japan Y. Takakuwa, Tohoku University, Japan |
| Correspondent: | Click to Email |
As a novel tool of plasma ion beam techniques for surface smoothing, we have developed a photoemission-assisted plasma ion source (PAP) [1]. It has been confirmed that the Ar+-PAP treatment has an effect to smooth mechanically grinded Al and Cu surfaces with an initial surface roughness (Ra(0)) of a few hundred nanometers [ 1 ]. To clarify the surface morphology changes by PAP ion source and understand the PAP ion source-surface interaction, in this study, Cu deposited on Si rare surface (Cu(200 nm)/SiR) with Ra(0) ~13 nm, has been used for surface smoothing treatments. Plasma parameters have been measured by a cylindrical single Langmuir probe to better understanding the characteristics of the PAP.
In the experimental apparatus of PAP, a Xe excimer lamp with UV light (λ = 172 nm) was employed, leading to the order of 1012 photoelectrons/cm2/s, which enabled us to generate uniformly glow discharge over 2-inch Si wafer at bias voltage VB of 200 V under Ar atmosphere with pressure of 300 Pa, and to increase a discharge current up to 10-6-10-4 A at smaller VB than 200 V, which is referred to as Townsend plasma. According to the plasma potential measured by Langmuir probe, taking the energy loss due to elastic collisions between Ar+ ion and Ar atom into account, we estimated the Ek of Ar ion upon the impingement with the substrate to be 10.7 and 0.79 eV for glow and Townsend discharge, respectively. Based on the estimated values of Ek, a surface flattening model of the dry planarization process is discussed.
When the Cu surfaces irradiated by the photoemission-assisted glow discharge plasma (Ek = ~10.7 eV), and the photoemission-assisted Townsend discharge (Ek = ~0.79 eV), the surface roughness was improved down to ~69.8% and ~54.5%, respectively. It indicated that the PAP has the ability to reduce the surface roughness down to atomic-scale under both discharge conditions. It has been reported that diffusion barrier of Cu atom via hopping or exchanging on Cu surface is 0.04 ~ 0.66 eV [2] and the threshold energy of Cu sputtering by Ar+ is between 25~50 eV [3]. Therefore the enhancement of surface migration of Cu atoms is mainly responsible for the improvement of Ra in discharge conditions. Conclusively it is considered that the photoemission-assisted plasma works as an ion source with Ek in the order of eV, which sufficiently makes the surface morphology improved due to the enhancement of surface migration.
Reference
[1] Y. Ohtomo, S. Ogawa, and Y. Takakuwa, Surf. Interf. Anal. 44 (2012) 670.
[2] J. Wang et al., Modelling Simul. Mater. Sci. Eng. 12 (2004) 1209.
[3] J. D. Kress et al., J. Vac. Sci. Technol. A 17 (1999) 2819.