Studies On Properties And Application Of Novel CMP Pad And Slurry

Chemical-mechanical polishing (CMP) is widely used in planarization of silicon substrate and multilayer metal interconnection construction and becomes one of core technologies in ULSI fabrication. With the decrease of feature size and the increase of integration level of IC chip, CMP technology is facing higher demand and new challenge. The present CMP technology is incapable of meeting the needs of wafer surface quality in next generation IC. It is important to research and develop new CMP technology to meet the global sustainable development.The CMP process is well recognized as the best and only technology in providing global planarizations for wafer processing. However, CMP processes also have disadvantages in terms of introducing defects such as dishing, erosion, scratches, and contamination etc. In order to solve these problems, vary of methods such as fixed abrasive pad, free abrasive and electrochemical mechanical planarization (ECMP) have become the hot spot in present study. Based on the modified CMP pad and developed slurry, vary of reactive components were added to the pad and a new chelating agent was included in the slurry in order to improve the polishing effect. Series of research on the mechanism and effect of using these new methods have been studied.During polishing, CMP pad carries the slurry and transmits the normal and shear forces. Also CMP pads are generally designed to play a passive role in terms of chemical reactions that occurr on the surface to be polished. For metal CMP, in order to have a higher removal rate, adusting polising pressure and impoving the chemical reaction are the main methods. With the conventional process, polishing pressure must be maintained at a fairly high level to obtain a high removal rate. However, such a high polishing pressure is one of the dominant reasons for defects such as dishing and erosion. A common approach to this issue is to increase the chemical reactivity of slurry to balance the need for a high removal rate and low defects at low polishing pressures. For this work, glycine and 1H-Benzotriazole (BTA) was incorporated into the pad separately in order to impove the chemical reaction on material surface. From the results of polished pattern wafer, glycine was released from the pad and strated to have a reaction with copper in the protrude area. With the help of mechanical force, as the protruding areas on the wafer make greater contact with the glycine and pad, a higher removal rate was obtained. Meanwhile, the lack of contact for the areas in the low areas on the patterned wafers translates to lower removal rate. Defects happened on the surface somehow decreased. In contrast, based on the dishing and erosion results, the BTA molecules were released from the pad tip, which, when passing through the recessed areas, the amount of BTA in these areas increases.Viewed from this angle, the higher removal rate was obtained at higher areas because of the lack of protection by the BTA. The lower area is well protected by the higher amount of BTA. The lack of contact areas in the low areas on the patterned wafers translates to a lower removal rate. The differential removal rate created by such functional pad surfaces is able to improve the SHRE and to minimize the dishing and erosion. Results indicate that glycine and BTA have different mechanism on copper CMP. Glycine tends to react with the higher area, however, BTA tends to simulate in the lower area after they are released.Glycine is the most effective chelating agent which is widely used in copper CMP at present due to glycine can provide ideal removal rate. However, the possibility of introducing defects on the surface will be increased. In order to minimize various defects, passivating agents have been commonly used in the slurry containing glycine. In this work, an organic chemical, 6-Methyl-1,3,5-triazine-2,4-diamine will be the very first time to apply on copper CMP. Based on the nitrous lone-pair electron in triazine ring and amino group, copper ion will be complexed and expelled from the surface in term of copper complex. Due to methyl group and ring structure is hydrophobic, the solubility of the copper complex is limited. In the other hand, the ring structure can stick on the surface and form a protective film, with the help of hydrogen bond, the thickenss of the protective film tends to be thicker. Based on this film, TA has a potential in minimize defects. Results from polished pattern indicated that, in the case without passivating agent, TA slurry can decrease the formation of vary of defects.In order to further improve the performance of TA slurry on polishing, 1,2,4-triazole, 1,2,3-triazole, BTA, Benzimidazole(BIA), 5-Phenyl-1H-tetrazole were employed as passivating agent to cooperate with TA to obtain the better surface quality. At pH 4, the best polishing quality was given by the BTA and TA slurry. Meanwhile, due to BTA does not provide effective passivation of recessed Cu surfaces at low pH, where the azole ring becomes protonated, the improved low-pH passive film formation for PTA in Cu CMP slurries relative to BTA is most likely due to its much lower pKa (4.3), with a much larger fraction of PTA in the anionic form at low pH. In the help of PTA at low pH, the surface quality is somehow impove with the higher removal rate.