AVS 50th International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS2-ThM

Paper PS2-ThM5
Control of Degradation Thickness on SiOCH Surface

Thursday, November 6, 2003, 9:40 am, Room 315

Session: Low k Dielectric Etch
Presenter: T. Tatsumi, Sony Corporation, Japan
Authors: T. Tatsumi, Sony Corporation, Japan
T. Saitoh, Sony Corporation, Japan
A. Ando, Sony Corporation, Japan
K. Nagahata, Sony Corporation, Japan
Y. Morita, Sony Corporation, Japan
Correspondent: Click to Email
We investigated ashing technologies for low-k/Cu integration. SiOCH film oxidizes easily forming a degradation layer that must be minimized to suppress the CD variations during wet treatment. We used an ashing system using ICP and evaluated the ashing rate, residue, and the thickness of the damaged layer (T@sub d@) on the side-wall of the SiOCH via hole. When we used H-based plasma for ashing, T@sub d@ was relatively thin. However, it was difficult to maintain a high etch rate and to remove the residue completely. Hence, we had to use O-based gas chemistry in mass production. Using O@sub 2@ plasma, T@sub d@ depended on (a) the O radical density, (b) the thickness of the C-F polymer formed on the sidewall during via etching, and (c) wafer temperature. The density of O radical depended on the partial pressure of O@sub 2@ and dissociation degree of O@sub 2@, which could be related to the number of collision with electrons: N@sub e@<@sigma@v>, where N@sub e@, @sigma@, and v were electron density, collision cross-section for dissociation, and electron energy, respectively. We estimated N@sub e@<@sigma@v> from the intensity of the optical emission of Ar (750 nm, I@sub Ar@=N@sub Ar@N@sub e@<@sigma@v>) and we found that the ashing rate, as well as the thickness of the damaged layer under various conditions, clearly depended on the "partial pressure of O@sub 2@" x "I@sub Ar@/N@sub Ar@". When we minimized the radical density by using low density (< 6 x 10 cm@super -3@ ) and low pressure (< 3Pa) conditions, the thickness of the damaged layer could be suppressed below 10 nm while the ashing rate was higher than 500 nm/min with no residue. To fabricate reliable Cu interconnects, we not only need to etch various low-k materials, but also quantitatively control the degradation of these materials.