AVS 52nd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuA

Paper PS-TuA3
Influence of Plasma Modulation on low-k Etching in High Density Fluorocarbon Plasmas

Tuesday, November 1, 2005, 2:40 pm, Room 302

Session: Dielectric Etch II
Presenter: V. Raballand, Nantes University, France
Authors: V. Raballand, Nantes University, France
G. Cartry, Nantes University, France
C. Cardinaud, Nantes University, France
Correspondent: Click to Email
Low dielectric constant materials (low-k) are used as interlevel dielectrics in integrated circuits. Materials studied are porous and non porous methylsilsesquioxane polymers (SiOCH), as well as amorphous hydrogenated silicon carbide (SiCH), used as hard mask and/or etch stop layer. We study the influence of bias, and source power modulation on low-k etching in high density CHF@sub 3@ based plasma. In addition, low-k etching mechanisms are investigated by using plasma diagnostics (OES, Langmuir probes) correlated with surface analysis (XPS). We use a 13.56 MHz Inductively Coupled Plasma source mounted above a diffusion chamber where the substrate is biased separately. Etch rates are measured in real time by in-situ multi-wavelength ellipsometry. First, only the bias voltage is pulsed. By decreasing the duty cycle (dc), the threshold between etching and deposition is shifted toward higher bias voltage. Moreover, this threshold common for all materials in continuous mode (around - 40V), is now equal to - 50V for porous SiOCH and - 80V for SiCH when pulsing at 1kHz with dc=0.45. Selectivities exceed 10 on a large bias window (50V), while they only reach 6 in continuous mode. Then, we simultaneously pulse the source power and the bias power. Low-k etch rates and selectivities are measured for various ON-time and OFF-time periods. We observe that when the ON-time period is smaller than the time for the plasma to be in stable regime, selectivities are enhanced. To complete these studies, some pattern transfers are realized and compared in continuous and pulsed modes (pulsed bias, or pulsed bias and plasma). Finally, surface compositions and plasma characteristics are analysed. Etching mechanisms are determined in pulsed and continuous modes.