Effect of Top Power on low-k damage during oxygen strip in a TCP etch chamber Eddy Kunnen a , D. Shamiryan a , H. Struyf a , W. Boullart a , M. R. Baklanov a a IMEC, Kapeldreef 75, Heverlee 3001, Belgium The modification of a SiOCH based low-k by an oxygen plasma in a Transformer Coupled Plasma (TCP) is studied. The damage is studied as function of TCP power and time. Optical emission spectroscopy (OES) indicates that adding TCP power increases the O/O 2 + ratio in the plasma. By means of OES, evidence is found for removal of hydrogen out of the low-k during plasma exposure, which is confirmed by FTIR measurements. Spectroscopic ellipsometry (SE) measurements in the 150-750 nm range show that the damage depth increases with TCP power. FTIR and SE are in accord. The density and refractive index found out of SE and mass measurements decreases with top power. As a function of time a logarithmic thickness dependence of the damaged layer is found. Introduction One of the key challenges for introducing low-k materials into IC manufactory is to limit the negative impact of plasma etch and strip processes on these materials [1]. Degree and nature of plasma damage depends on several factors. The most important are chemical interaction of active radicals with hydrophobic groups, modification of low-k by ion and UV radiation etc. The separation of these factors in standard etch and strip systems is normally difficult. For this reason, we focus on an oxygen strip applied in a TCP chamber on a SiOCH based low-k with a k value of 2.3 as function of TCP power and time. Adding TCP power we were able to change the O/O 2 + ratio in the plasma. Plasma properties are investigated by OES. The damage induced in the low-k is studied by SE, FTIR and mass measurements. Top power is varied and photo resist (PR) etch rates are determined to normalize the exposure times to an equivalent PR removal between 6- 700 nm. As will be shown damage depth increases with TCP power. Experimental A 190 nm thick SiOCH layer is deposited on top of 300 mm Si wafers and the porogen is removed by UV curing. The plasma exposure is carried out in a Lam 2300 Star etch chamber keeping O 2 flow, pressure and bottom power constant. The OES is recorded by the standard spectrometer of the tool. The centre point of the wafer is measured by SE in the range of 155-780 nm and fitted based on a two layer model. FTIR is taken in nitrogen ambient between 400-4400 cm -1 . Finally the mass is measured on a mentor tool from Metryx. Results and discussion Fig. 1 shows the experimental conditions and composition of the layer. Damage increases with TCP power and exposure time. When running the process conditions on an oxide wafer, fig. 2 indicates that O radicals become relatively more abundant than the O 2 + ions with increasing TCP power. If the same conditions are applied on a low-k wafer, than for the conditions with top power a variety of emission lines, as from hydrogen, is seen during the first seconds, fig. 3. Fig. 4 shows that the FTIR Si-CH 3 peak area scales with the damage depth as obtained from SE and fitting a two layer model. Damage as function of exposure is shown in fig. 5. The dependence is closer to a logarithmic than a parabolic behavior as can be seen from fig. 6, indicating a more complicated oxidation limiting mechanism than solely the diffusion of oxygen radicals as in the case of downstream reactors. The density of the damaged layer and the refractive index are shown in fig. 7. The density of the damaged layer decreases with increasing TCP power. In summary lowering the TCP power gives a less thick and denser damaged layer. The oxidation follows a logarithmic behavior as function of time. Conclusions In conclusion it can be stated that adding TCP power increases the O/O 2 + ratio in the plasma. Low TCP power results in a denser and thinner oxidized layer on top of the low-k. Kinetic equations and mechanism of the observed phenomena will be discussed. References [1] K. Maex et al, J. Appl. Phys. Vol 93, Iss. 11, p. 8793, (2003) corresponding author e-mail: Eddy.Kunnen@imec.be