Effect of Sodium Periodate in Alumina-Based Slurry on Ru CMP for Metal–Insulator–Metal Capacitor

Abstract

In this study, a ruthenium ͑Ru͒ chemical mechanical planarization ͑CMP͒ slurry was developed and characterized to fabricate Ru bottom electrodes in capacitor structures. Sodium periodate ͑NaIO 4 ͒ was chosen as both the oxidant and etchant due to its strong oxidizing power. The effect of NaIO 4 on Ru etching and polishing behaviors was investigated as a function of its concentration and polishing condition. The largest removal rate of 70 nm/min was obtained in a slurry of 0.1 M NaIO 4 and 2 wt % alumina particles at pH 9 and a polishing pressure of 4 psi. Planarization and isolation of each capacitor was successfully performed with the developed Ru slurry.In dynamic random access memory technology, a conventional capacitor has a semiconductor bottom electrode that is called a metal-insulator-semiconductor capacitor. However, a conventional poly-Si bottom electrode cannot satisfy the requirement of electrical properties and compatibility with high-k materials. For this reason, a metal-insulator-metal capacitor has been investigated. 1,2 Noble metals can be used as bottom electrodes of capacitors because they have a high work function, and thus provide a high barrier for leakage current. In addition, they are chemically very stable. Among different metals, Ru has been suggested as an alternative bottom electrode due to its excellent electrical performance, including a low leakage of current and compatibility with high dielectric constant materials. 3 Ru film has also been actively investigated as a Cu diffusion barrier metal for Cu interconnection due to its good electrical conductivity, immiscibility with Cu, and good adhesion property to Cu layer. 4,5 To isolate and planarize a Ru bottom electrode, dry etching technology has been widely used. 6 However, the dry etching method generates several problems such as Ru excessive recess or a loss of oxide. These problems, in turn, cause a current leakage or loss of capacitance. Therefore, a chemical mechanical planarization ͑CMP͒ process has been suggested to planarize and isolate the bottom electrode. 7 Though there is a great need for the development of a Ru CMP slurry, few studies have been carried out due to its noble properties against chemicals. If a Ru surface can form RuO 4 or RuO 2 ·2H 2 O in a chemical, it would be possible to design slurry chemistry for Ru because RuO 4 is a soluble oxide in aqueous solution. 8 In organic chemistry, periodate ion ͑IO 4 − ͒ is a well-known oxidant. 9,10 It has been reported that sodium periodate ͑NaIO 4 ͒ can form RuO 4 from hydrated ruthenic oxide ͑RuO 2 ·nH 2 O͒. 11,12 In this study, we tried to develop a stable slurry that has the characteristics of a high removal rate without a Ru attack. For this purpose, NaIO 4 was chosen for the preparation of the Ru CMP slurry. The static etch rate, passivation film thickness, and wettability were measured as functions of the slurry chemical concentration. In addition, the effect of chemicals on polishing behavior was investigated as a function of chemical concentration, abrasive parti...

Study of bimetallic corrosion related to Cu interconnects using micropattern corrosion screening method and Tafel plots

“…In addition, ruthenium (Ru) and other noble metals have been actively investigated for use as new diffusion barrier materials for Cu interconnects [10][11][12][13][14]. The increased noble character of diffusion barriers like Ru can further intensify the Cu galvanic corrosion in CMP chemical environments.…”

Surface characteristics of ruthenium in periodate-based slurry during chemical mechanical polishing

“…To achieve a satisfactory polished surface as well as good MRR selectivity between copper and ruthenium, periodate salts, hydrogen peroxide, potassium bromate as well as oxone have been investigated as the oxidants [14,[18][19][20]. Among the oxidants mentioned above, periodate salts have proved to be the most suitable oxidants with the MRR of over 50 nm/min in alkaline slurries [21,22]. Nevertheless, the presence of sodium in the manufacturing process of integrated circuit is usually not preferred.…”

Tribocorrosion Study of Copper During Chemical Mechanical Polishing in Potassium Periodate-Based Slurry

“…Many oxidants such as iodate, hydrogen peroxide, ammonium persulfate, and periodate have been used in the Ru polishing process [12][13][14][15]. Among them, potassium periodate is the most widely used oxidant, and several investigations into the copper CMP process in periodate-based slurries have been carried out in recent years [16,17]. These studies have mainly focused on the aspects like chemical and mechanical material removal, the surface quality, and the control of galvanic corrosion.…”