Nanoscale Defect Generation in CMP of Low-k/Copper Interconnect Patterns

Abstract

Chemical mechanical polishing ͑CMP͒ can lead to nanoscale damage in films and surface features due to normal and lateral deformations of the surface. Defects arise due to the synergistic effects of chemical and mechanical mechanisms. This occurrence increases with severity as feature sizes are on the same order as abrasive polishing particles and materials decrease in stiffness, as with advanced low-k dielectrics. Here, relationships describing the response of normal and lateral surface deformations have been developed experimentally and from contact modeling. This is achieved by atomic force microscopy nanoscratching with diamond tips in a KOH environment to simulate CMP processing conditions. The deformations are related to the applied normal load, friction coefficient, film properties, and line densities. The deformations are observed to have critical loads of 1 and 5 N associated with normal and lateral deformations, respectively, which are on the same order as actual CMP particle pressure estimates.There exists an ever increasing need in the semiconductor industry to reduce the size of an integrated circuit ͑IC͒ while improving its performance. This has been achieved by producing multilevel structures and using advanced materials. 1 With the use of layered structures, the formation of nonplanarized surface topography during fabrication is a challenge. Chemical mechanical polishing ͑CMP͒ has been developed intensively and has shown a dynamic growth, playing a key role in the semiconductor industry because it is not only an efficient planarization process but also an effective way of removing wafer surface defects. CMP has allowed the improved lateral circuit dimensions to minimize interconnect delay, 2 and the minimization process has been achieved by the transition from aluminum to copper metal interconnects and from traditional dielectric SiO 2 to low-k ͑LK͒ or ultralow-k ͑ULK͒ dielectric materials. 3 However, the adoption of porous LK materials has brought implementation problems, such as delamination of dielectric materials during CMP due to poor adhesion between layers, poor mechanical strength of porous LK interlayer dielectrics, 4 low thermal conductivity, and incompatibility with existing IC manufacturing processes. 5,6 The formation of surface defects on LK interlayer dielectrics during CMP affects local, near-neighbor structures as well as multilevel structures after subsequent process steps, leading to decreased reliability and performance degradation.Many researchers have worked to investigate LK dielectric material delamination and wear. 7-14 Busch and Hosali 15 observed structural and chemical modifications of LK materials due to CMP operating conditions, whereas Balakumar et al. 16 performed CMP on Cu/SiLK single-and dual-stack nonpatterned wafers to study fundamentals of delamination during CMP, and Leduc et al. 17 measured the dependence of CMP-induced delamination on LK dielectric film stacks and established a relationship between delamination and the number of ULK dielectric layers.In addit...

Chemical and Mechanical Aspects of a Co-Cu Planarization Scheme Based on an Alkaline Slurry Formulation

“…18,19 To fully utilize these alkaline slurry chemistries, new advances have been made in recent years, 20,21 which include strategies for tackling alkaline damages to low-k materials. 22,23 In view of these developments, alkaline (pH = 10.3) slurry solutions are employed in z E-mail: samoy@clarkson.edu the present study. Sodium bicarbonate is frequently used as a standard pH adjuster, 24,25 but the main reason for considering this additive in the current work is to utilize its well-known complex-forming ability with Co 26,27 as well as Cu.…”

Passivation Kinetics of 1,2,4-Triazole in Copper Chemical Mechanical Polishing

“…With the development of ULSI, porous ultra-low-κ dielectric with a low mechanical strength is integrated in copper interconnects, and as a result, much weaker mechanical stress can be used in the copper CMP process to avoid severe damage to the copper damascene structure. [46][47][48][49] However, as can be concluded above, with the conventional inhibitor BTA, a high mechanical stress is demanded to achieve a high copper MRR of 5000 Å/min or larger. 10 In order to maintain a sufficient copper MRR under such a low mechanical stress, an inhibitor with a weaker passivation ability than BTA should be used as a substitute.…”

Scratching of Patterned Cu/Dielectric Surface Layers by Pad Asperities in CMP

“…First, the small abrasives may agglomerate due to fluctuations in slurry delivery, inter-particle attraction, etc. Scratches generated by the agglomerated particles are termed surface defects, because the size of these scratches will be an order of magnitude greater than of those created by individual abrasive particles [7]- [11]. Second, scratches can also be generated by pad asperities in direct contact, under certain conditions.…”