At SEMICON West this year, July 14-16 in San Francisco, the Chemical and Gas Manufacturers Group (CGMG) Committee of SEMI have organized an excellent program covering “Contamination Control in the Sub-20nm Era” to occur in the afternoon of the 14th as part of the free TechXPOT series. Recent high-volume manufacturing (HVM) developments have shown much tighter IC control specifications in terms of particles, metal contaminants, and organic contaminants. The session will present a comprehensive picture of how the industry value chain participants are collaborating to address contamination control challenges:
1. IDM / foundry about the evolving contamination control challenges and requirements,
2. OEM process and metrology/defect inspection tools to minimize defects, and
3. Materials and sub-component makers eliminating contaminants in the materials manufacturing, shipment, and dispensing process before they reach the wafer.
Updated reports about the markets for specialty electronic materials have recently been published by the industry analysts at TechCet, including topics such as ALD/CVD presursors, CMP consumables, general gases, PVD targets, and silicon wafers. Strategic inflection points continue to appear in different sub-markets for specialty materials, as specifications evolve to the point that a nano-revolution is needed. One example is TechCet’s recent reporting that 3M’s fixed-abrasive pad for CMP has been determined to be unable to keep up with defect demands below 20nm, and is undergoing an orderly withdrawal from the market.
As reported in more detail at Solid State Technology, during the IEEE IITC now happening in Grenoble, imec and Lam showed a new Electroless Deposition (ELD) cobalt (Co) process that is claimed to provide void-free bottoms-up pre-filling of vias and contacts. The unit-process is intended to be integrated into flows to produce scaled interconnects for logic and DRAM ICs at the 7nm node and below. Co-incidentally at IITC this year, imec and Lam also presented on a new ELD copper (Cu) process for micron-plus-scale through-silicon vias (TSV).
The bulk resistivities of metals commonly used in IC fabrication are as follows (E-8 Ω⋅m):
Cu – 1.70,
Al – 2.74,
W – 5.3, and
Co – 5.8.
Of course, the above values for bulk materials assume minimal influence of grain sizes and boundary layers. However, in scaled on-chip interconnect structures using in today’s advanced ICs, the resistivity is dominated by grain-boundaries and interfacial materials. Consequently, the resistivity of vias in 7nm node and beyond interconnects may be similar for Cu and Co depending upon the grain-sizes and barrier layers.
The melting temperatures of these metals are as follows (°C):
Al – 660,
Cu – 1084,
Co – 1495, and
W – 3400.
With higher melting temperature compared to Cu, Co contacts/plugs would provide some of the thermal stability of W to allow for easier integration of transistors and interconnects. Seemingly, the main reason to use Co instead of W is that the latter requires CVD processing that intrinsically does not allow for bottom-up deposition.