Applied materials copper roadmap

03/01/1998

Applied Materials`copper roadmap

Applied Materials recently issued its roadmap for copper interconnect technology, and announced that it plans to offer an entire suit of process solutions over the next several years. In a first move, the company released a new Endura Electra Cu system for the deposition of barrier and seed layers. The new product combines ionized-PVD (termed "Electra IMP") modules for Ta or TaN barriers and for Cu seed layers. The company also stated that it will develop a copper electrochemical deposition (ECD) tool.

Copper is a very stable metal, and it is difficult to find a volatile byproduct of any chemical reaction to enable economical dry etching. However, copper can be very easily removed by CMP. Thus, almost all copper development focuses on the metal damascene process flow that is based on oxide etch, blanket metal deposition to fill lines/vias, and CMP to remove excess metal. (See "Processing and integration of copper interconnects," p. 49, for a complete discussion of copper integration.)

Since trace amounts of copper can easily degrade active device performance, continuous barrier layers are needed to separate the metal interconnect structures from the active regions. Also, both ECD and PVD need some manner of "seed" or "wetting" layer to allow for the proper fill of fine structures.

ECD is widely acknowledged as the process of choice for the main damascene fill process in the first generation of interconnects built with pure copper instead of aluminum alloys. Semitool is the only company that has a production worthy ECD system on the market today, but CuTek (the startup lead by Chiu Ting in Sunnyvale, CA) plans to field systems this year, and now the largest company in the world is entering the market. Ashok K. Sinha, president of Applied Materials Metal Deposition Product Business Group, stated, "We have an electroplating program in place to have beta-tools delivered in 1998."

In addition to ECD, Applied Materials has groups working on ionized-PVD Cu for seed/wetting layers, and on PVD for the fill. Surprisingly, the company`s copper roadmap calls for PVD fill to replace ECD within one generation (see table). ECD is already designed into the process flow for 0.18 ?m, so it`s too late today to try to sell customers on copper PVD fill. However, the company claims that PVD-based processes are extendible down to at least 0.13 ?m, and the process may be more robust than ECD.

The ECD seed layer will be PVD copper. If the world switches to PVD copper fill, then - ironically - PVD copper will not work as the wetting layer. CVD copper will be needed since the material properties of the wetting layer are critical for successful PVD fill of deep-submicron structures. Sinha stated, "PVD surfaces may not be as atomically smooth as CVD."

The barrier layer can be produced by PVD down to 0.15 ?m. From 0.13 ?m and lower, however, CVD will be needed. Metalorganic CVD precursors react on the exposed surfaces of structures, not in the gas-phase, so the deposition is nearly perfectly conformal and can uniformly coat the insides of 0.13 ?m high aspect-ratio gaps. - E.K.