Advanced interconnects face big issues for 0.18 micron
09/01/1997
Advanced interconnects face big issues for 0.18 micron
Though 300-mm wafer processing was the biggest draw at the vast majority of show booths, the biggest changes to the equipment and materials industry may come from the fundamentally new technologies that will be required to fabricate ICs with 0.18-micron minimum line-widths. DUV lithography seems to be sufficiently extendible to 0.18 micron, but the fabrication of new interconnect layers and ultra-shallow junctions pose particular problems.
Electrochemical copper deposition. Copper lines in a damascene architecture will definitely be needed by the 0.18-micron generation. The top metal lines (with relaxed aspect ratios) may be deposited by simple PVD, but lower layers will almost certainly require a technique that can fill aggressive aspect ratios. The two most likely processes are CVD and electrochemical deposition (see "Electrochemical planarization of ULSI copper," Solid State Technology, June 1997, p. 155).
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Figure 1. Semitool`s LT-210 electrochemical copper deposition system.
Despite years of development, copper CVD requires metalorganic precursors, and no company has yet succeeded in developing a production-worthy process. However, Semitool, Kalispell, MT, had a beta-version of its new LT-210 electrochemical copper deposition system to show customers in an inner room of its booth (Fig. 1). Based on the company`s established single-wafer wet-processing technology, the system has two rows of five single-wafer stations (10 total) with deposition and pre-deposition wet-etch divided between them.
The company claims that the system produces >60 wph with high purity, large grains, and low resistivity, in a 57 ft2 footprint. The LT-210 platform`s ambient temperature deposition allows device manufacturers to introduce copper without degrading the heat-sensitive polymers that are likely to be needed as low-k dielectric layers. The copper barrier and seed layers will require a different deposition technique, most likely CVD.
Metalorganic barrier layers. Novellus, San Jose, CA, has used the same idea that started the company over a decade ago - sequential processing - to produce a new CVD system for complex metalorganic precursors (Fig. 2). The "Prism" system`s dual plenum gas distribution system delivers tetrakis (diethylamino) titanium (TDEAT) and NH3 precursors to produce TiN barrier layers that are compatible with copper metallization.
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Figure 2. Novellus` Prism system
TiN films deposit below 350?C, with 70 percent sidewall coverage in high-aspect-ratio structures and uniform film properties from field to tight gaps. Throughput is reportedly >50 wph, resulting in cost of ownership of $2/wafer. The Prism system is reportedly in pilot production at customer sites with multiple repeat orders. Depending on the configuration, the system costs at least $2 million.
Novellus showed a small, but significant, processing module for new materials. For low-k spin-on dielectrics that require a PECVD capping layer, the company designed a simple bake module to drive off adsorbed water without reducing system throughput. The module doesn`t perform densification or stabilization bakes.
Novellus also showed the latest offering from its thin-films group recently acquired from Varian: the Inova PVD system (Fig. 3). Designed around Varian`s latest implant platform, with slick new software, the system features improvements to the sputter source, electrostatic chuck, and chamber materials. - E.K.
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Figure 3. Novellus` Inova PVD system.