by Ed Korczynski, Senior Technical Editor
The latest evolution of Novellus Systems Inc.’s 300mm wafer Vector Express PECVD tool reduces the number of deposition zones to actually increase the system throughput for thin films. With >70% of the 45nm dielectric PECVD for logic (see figure, above) and >50% for DRAM being <100nm thin, the time spent in deposition itself can be less than the handling or heat up. Thus, the first of the four sequential stations in the system has been converted to allow for "smart-soak" temperature stabilization. Improved handling subsystems allow throughput to increase 10%-50% compared to any of the >600 prior generation Vector tools shipped since 2000.
For relatively thick films such as a silicon nitride layer, processing throughput is dominated by the deposition time itself. For ultra-thin films, such as 10nm-20nm of TEOS-based oxide, the deposition time in each of the three stations is only 3-5 sec, but it takes 10sec to first heat the wafer up to deposition temperature.
Defects and thickness uniformity both improve with extended soak-times — for example, increasing soak-time 4X over a nominal baseline reduces particles >0.12µm to the single single-digit range. The soak-time ensures temperature uniformity, and also allows for outgassing from lower dielectric layers, to ensure good adhesion of a SiC dielectric cap on top of a low-k dielectric for example.
The new tool’s liquid delivery system includes different injection nozzles to accommodate different precursors for different liquids, so as to create ALD-type response times for CVD processes. “We can replicate results to 6nm thin TEOS films,” explained Tim Archer, SVP of Novellus’ dielectrics business group, in an exclusive interview with WaferNews. “No one has use for it today, but we have it.”
The improved handling hardware, including lift-pins, pedestals, gate-valves, and pumps can be field-retrofittable, and the faster handling results in >10% claimed greater throughput even for thick films using all four deposition stations, Archer noted, adding that the Vector Express has better cost-of-ownership across all dielectrics compared to the prior generation Vector. The company already has orders for >20 systems since the first beta tools were placed in 3Q06. — E.K.
FIGURE CAPTION: Over 70% of the PECVD for 45nm node logic are for films <100nm thin, calling for different OEM tools to optimize fab throughputs. (Source: Novellus Systems)