Study on the cleaning of silicon after CMP in ULSI

Abstract

In this paper, the cleaning of silicon after CMP (chemical mechanical polishing) in ULSI was studied utilizing preferential adsorption knowledge. On the basis of analyzing adsorption state of contaminated particles on polished silicon wafer and interrelated adsorption theory, the preferential adsorption model is put forward: t=k r 2 (f 1f 2S) . Non-ion surfactant is chosen and acts as the second kind of adsorbate, which is preferentially adsorbed onto the polished silicon wafer. The second kind of adsorbate can effectively depress the surface energy of new polished silicon wafer, form a layer of protective film and prevent the chemical adsorption and bonding of the contaminated particle near the surface of polished silicon wafer. In addition, a new kind of chelant, being a free metal ion, is also added in order to chelate and wipe out the metal ion on the polished silicon wafer. Consequently, the organic impurity, impurity particles and metal ion on the silicon surface were wiped out effectively and the silicon has a pure surface after cleaning. The results of cleaning experiments show that the chemical cleaning method in this paper can control the adsorption state of particle on the polished silicon wafer and cause the adsorption state to remain at the physical adsorption state for a long time: even after 168 h in the surfactant solution the wafers reach the SEMI standard after being washed.