Semiconductor fabs move toward integrated processes delivered through suppliers

01/01/1999

Semiconductor fabs move toward integrated processes delivered through suppliers

Thomas M. Parrill, Peter DiSessa, Eaton Corp., Beverly Massachusetts

The drive to continue the semiconductor industry`s remarkable productivity rate increase is transforming the entire supply chain. Companies at all points along the "food chain" are expanding the scope of their activities, while attempting to remain focused on their core competencies. Three examples illustrate this trend toward a broader scope of involvement:

1. the immensely successful foundry fabs are acquiring intellectual property cores in order to offer design services;

2. semiconductor equipment providers are entering strategic alliances with complementary equipment partners or pursuing mergers in order to access the capability and knowledge necessary for process module development; and

3. some providers of components used in semiconductor equipment are taking responsibility for design and construction of major subsystems, such as vacuum or gas delivery manifolds.

While perhaps no one can predict the extent to which this transformation will occur, it is evident that companies are changing their business models to remain competitive.

In recent years, this evolution has spurred equipment suppliers to develop unit process expertise to augment their equipment expertise. Many IC manufacturers cannot cost-effectively allocate the time or resources to investigate each and every unit process application from scratch. In addition, when problems in the manufacturing process do occur, an equipment supplier with process expertise can often suggest solutions based on a thorough understanding of the equipment operation. This trend is and will be evident as equipment suppliers develop knowledge pertaining to groups of related unit processes - that is, processes that occur near each other in a process flow, or that have a particularly strong interaction. The extension of unit process expertise will allow IC manufacturers to save additional valuable time in process development, process start-up, and fab operations improvement. The need to provide this unit process and specialized process integration expertise continues to drive the significant changes taking place in the equipment supplier segment of the industry.

Before proceeding with a more specific discussion, it is important to stress that the process integration trend is motivating equipment suppliers to acquire, develop, and apply extensive process knowledge in order to serve their customers with the emphasis on custom. This trend does not involve the development of "off-the-shelf" processes. IC manufacturers will continue to concentrate on process technologies that they consider critical. They will investigate the key process steps in detail, and their resulting approaches will be unique intellectual property. For process steps that are not considered critical or differentiating, an extensive process development effort may not be justified, however, and more support is therefore expected from equipment suppliers.

The development of ultrashallow junctions for transistors with critical dimensions at or below 180 nm offers a good example of the interplay between ion implantation and rapid thermal processing (RTP) in particular (see sidebar "An example: Eaton`s approach" on p. 000). Recent work illuminating the effects of transient-enhanced diffusion and boron-enhanced diffusion has shown the need for boron ion implantation energy <1 keV, faster RTP ramp rates, and "spike" RTP anneals. If these developments are not integrated wisely, however, the desired result, an ultrashallow junction with a reasonably low sheet resistance, will not be achieved. Furthermore, there are several possible implant/RTP conditions leading to the same point on the junction depth-sheet resistance map: An equipment supplier with experience in both processes plus a good understanding of the fundamental materials science involved will be able to suggest alternative processes to achieve desired device parametric goals. An equipment supplier`s ability to provide process and process integration knowledge thus enables faster, more efficient process development for IC manufacturers. In a business climate of resource constraints and time-to-market pressure, chipmakers can succeed by leveraging the abilities and expertise of strategic equipment suppliers.

Considering operational issues, such as overall equipment effectiveness (OEE) or cost-of-ownership during the development phase, is another fruitful area of cooperation between chipmakers and equipment suppliers. Working with a key supplier possessing unit process and basic process integration knowledge expands the scope, and therefore the possibilities, for efficiency improvements. These benefits will translate into future dollars as the process is transferred to manufacturing and ramped to large volume. Many IC companies, for example, are investigating the use of high-dose buried layers (HDBLs) as a replacement for the epitaxial silicon substrate. Published data indicate that the HDBL simultaneously improves latch-up immunity, enhances impurity gettering, and lowers total cost. But making a significant change to an existing process flow requires extensive integration investigation, which can be done faster and more efficiently if the high-energy implant supplier possesses modeling capability and understands subtle transistor and circuit performance effects.

Concurrently, IC manufacturers may save additional money by:

1. qualifying the high-energy implanter to run retrograde well and channel implants, such as the threshold voltage adjustment, and optimizing their implanter mix for best overall OEE; and

2. incorporating a residue-free, photoresist strip removal process, tailored for the thick resists required for deep implants, which allows significant reduction or elimination of the caustic chemicals traditionally used to clean wafers.

Again, increasing the breadth of the equipment supplier`s expertise through activity in the process integration regime promises new opportunities for productivity improvements.

An example: Eaton`s approach

The trend to integrate processes and process tools is driving productivity and efficiency improvements and has motivated Eaton Semiconductor Equipment Operations to expand its product offering and knowledge base. In addition to the Implant Systems Division, with its full range of ion implantation capability, the Fusion Systems Division provides advanced photoresist processing solutions, including photostabilization and resist strip, and the Thermal Processing Systems Division offers both rapid single-wafer and fast-ramp batch annealing processes. In several advanced process development applications, the interaction among these divisions is important, providing the ability to generate interdependent process data shared among them. Instead of focusing solely on ion implantation as a unit process, the focus expands to a doping sequence consisting of any or all of the following (see figure):

1. an optional photostabilization treatment providing improved photoresist integrity;

2. ion implantation;

3. a resist strip with chemical species designed to provide a residue-free surface; and

4. a RTP process to anneal and activate the dopant.

By expanding its capabilities in the doping sequences used to form integrated circuits, Eaton has enlarged the horizon of potential productivity benefits that may be realized by IC manufacturers, enabling quicker access to process data affected by multiple unit processes. Even in cases where the unit processes within a process sequence are orthogonal (do not strongly interact), documented data that demonstrate this are useful, since they allow for future flexibility in the process sequence.

THOMAS M. PARRILL is marketing manager and PETER DISESSA is marketing director at Eaton Semiconductor Equipment Operations, Eaton Corp., 55 Cherry Hill Drive, Beverly, MA 01915-1053; ph 978/232-4000, fax 978/232-4200.