Challenges and advances for CMP consumables
04/01/2004
In the early days of CMP, most of the focus was on developing the technology as a relatively stable process and enabling its usefulness, particularly for dielectric CMP. This was followed by tungsten CMP, which gained broad acceptance in the mid-1990s. Next came the adoption of copper CMP, followed by direct shallow-trench isolation (STI) polish. As new materials are continuously introduced, CMP innovation is expected to keep pace for polishing these materials (e.g., platinum).
With CMP widely accepted, the focus has shifted to increasing productivity: less downtime and development of new slurries and processes with higher removal rates and throughput. Yield enhancement, mainly through defect reduction, has also gained attention. This has been achieved through better manufacturing and design of slurries and pads, as well as polishing tool and process improvements.
Mechanistic understanding of CMP
Because end users are no longer content with accepting CMP as a black box, there has been significant emphasis on gaining mechanistic understanding of all aspects of the process — from tool upsets to slurry formulations to pad manufacturing. For example, the figure shows how removal rates on different films are affected by the various components in a barrier polish slurry. This kind of understanding serves two purposes. First, it allows users to pinpoint possible causes if a process upset is observed. Second, armed with this kind of understanding, the user and the supplier can work together to customize a product.
 Understanding of the effects of various components in a barrier polish slurry. |
Research has shown that different processes behave differently to the same inputs, so a design of experiments exercise conducted at a supplier's facility may not accurately reflect what happens at a fab. This underscores the need for close cooperation and characterization early on in the development process. If done correctly, this cooperation can shave months off development time and cause fewer upsets once the process has been put into manufacturing.
Process control expectations
Process control requirements for CMP have radically increased in the last few years, an important aspect being understanding and measuring all the key characteristics (KCs) for a given process. A pad or slurry supplier may identify hundreds of parameters for manufacturing control, but identifying the KCs is not a trivial effort. These KCs can extend from the point that slurries are delivered to the polisher all the way back to manufacturing of the raw materials for slurries and pads. The KC understanding and development process can also be facilitated by early and close cooperation between CMP users and suppliers.
The industry is also seeing the advent of techniques and tools that can measure slurry parameters close to the point of delivery. These are proving instrumental in providing early warning and heading off any process upsets before they occur. Sources of process upsets from polishing tools and diagnostics for these are not as well understood, however, and provide an opportunity for future improvement.
Finally, greater attention is being paid to driving the semiconductor industry's process control requirements throughout the CMP supply chain. Areas of focus include SPC, management of change, continuous improvement, and excursion management. A large fraction of CMP consumable suppliers and sub-suppliers have either never supplied or have only supplied bulk chemicals to the semiconductor industry. Given the complex nature of CMP and the demanding nature of the industry, the supply base as a whole needs to improve in this area.
Requirements for management of change, in particular, need to be driven throughout the supply chain. Small changes made at sub-suppliers, many of whom do not understand the need to control change, can have drastic consequences on CMP processes. Education of suppliers and sub-suppliers is needed. As the CMP industry continues to create new slurries and pads, end users need to understand the manufacturability of these new materials, some of which lead to very good process performance in R&D, but may never be manufacturable.
CMP has come a long way since its origin in the late 1980s. After an uncertain start, it has been firmly established as one of the key semiconductor processes as the industry moves toward the 65nm node. In this so-called "decade of materials," CMP consumables are playing a major role in enabling new processes. Progress in control and manufacturing of these materials needs to keep pace with improvements in performance.
For more information, contact Gautam Grover, global marketing manager, at Cabot Microelectronics Corp., 870 Commons Dr., Aurora, IL 60504; ph 630/375-5567, e-mail [email protected].