Chemically Impregnated Abrasives Provide High Planarization Efficiency Copper CMP Slurry

As device sizes decrease, next generation CMP slurries must achieve planarization on increasingly higher aspect ratio structures.  Current copper CMP slurries have a limited planarization efficiency (PE) (ratio of step height removed to thickness removed).  Without an improvement in PE, CMP is going to become an increasingly expensive and limiting step in the semiconductor manufacturing process.  Current commercial CMP slurries consist of homogenous mixtures of abrasives (typically metal oxide nanoparticles) and chemical components.  While incremental improvements to CMP performance using this paradigm continue to be obtained, new approaches to CMP slurry formulations will be needed to meet future device requirements.

General Engineering & Research, L.L.C. is developing a copper CMP slurry containing nano-sized contact release capsules (nano-CRC).  Instead of the traditional mixture of solid nanoparticles and chemicals, nano-CRC based slurries consist of a core-shell nanoparticle where the mechanical and chemical components are combined into a single entity (Figure 1).  When the nanoparticle contacts the wafer surface during CMP, the polymer coating is torn away and the chemical complexing agent (glycine) is released in an area localized to where it is needed.  In this research effort, nano-CRC particles made from porous colloidal silica abrasives were impregnated with glycine, and then coated with a polymer to encapsulate the glycine.  Upon shearing contact with the wafer surface during CMP, the polymer coating is torn away and the glycine is released.  The following development goals for a nano-CRC based slurry were met: 

1)      Chemical payload (glycine) encapsulated in the nanoparticle pores

2)      Stable polymer coating that prevented leakage of payload

3)      Polymer coating soft enough to be torn away by the shearing forces during CMP to release the payload

4)      Well dispersed particles that were free from agglomeration

5)      Cost effective manufacturing method for competitive CMP slurry pricing

To date, no known CMP slurry technologies have attempted to combine the mechanical and chemical components of the slurry into a single entity.  Initial results have yielded simultaneously high PE and high material removal rate (MRR), which will improve planarity and decrease processing costs. 

Table 1 summarizes the copper CMP results of the nano-CRC slurry compared to benchmark commercial CMP slurries.  Commercial slurries were diluted as recommended by the manufacturer, and a similar abrasion loading concentration was used for the nano-CRC slurry (equivalent of 4wt% abrasive).  Commercial Slurry A is an example of a chemical only slurry which is inexpensive but has only moderate performance (substantial etch rate, low MRR and low PE).  Commercial Slurry B has better performance with a negative etch rate and a MRR of 23 nm/min and a PE of 43%.  The best performing nano-CRC prototype was able to match the Slurry B etch rate and provide a 16 nm/min increase in MRR and a 24% increase in PE.  PE is a key factor in determining the surface quality after CMP (dishing) and the development of a class of very high PE CMP slurries will strongly impact future CMP utility.  Another consequence of high MRR and PE is their effect on the cost, time and waste stream of the CMP process.  The volume of slurry (Vol) needed to planarize a 200nm step height (ΔS) was calculated according to the following equation: Vol = (F ∙ ΔS)/ (MRR ∙ PE) (Table 1).   The nano-CRC slurry is predicted to require just 0.3 gal of slurry to achieve planarization compared to 0.8 gal of Slurry B, a 62% reduction in both slurry volume and time to planarize.  With further optimization, even greater improvements in the Cu CMP process is anticipated resulting in a product with a very high return on investment for semiconductor manufacturers.