Study Supports MEV, Cluster Tool Trend
By Meredith E. Lawrie
Greenville, SC–A “Strategic Fab of the Future” study conducted by Fluor Daniel (Greenville, SC) and Paul Castrucci and Associates (Burlington, VT) supports the growing trend toward using mini-environments (MEV) and integrated cluster tools as cost-effective and time-saving isolation techniques in clean environments.
In an attempt to evaluate the relationship between new IC technology and fab design and construction, Fluor Daniel contracted Paul Castrucci, former IBM plant manager and past CEO of SEMATECH, to develop a total-cost comparison, through computer simulation, of four “virtual factories”–three using Class 1 mini-environments in Class 10,000 work areas and the fourth using a conventional Class 1 ballroom design with tools in a bay-and-chase layout. According to the study, the most cost-efficient and profitable fabs were ultimately the three that used integrated cluster tools in Class 1 mini-environments.
Says Castrucci, “mini-environments provided several advantages. First of all, we didn`t have to control the whole ballroom at Class 1 or better–remember the goal is to control the wafer environment, not the room environment.” By putting the wafers in mini-environment pods and connecting the pod to the tool through an enclosure, the wafers only come into contact with a Class 1 environment.
Castrucci`s study also notes that because mini-environments allow for Class 10,000 work areas, they were able to save both money and time in gowning applications.
According to Castrucci, “you usually loose about an hour and 15 minutes a day to gown and de-gown. In a factory where I worked, which employed about 350 people, we saved about $1.7 million a year by converting from space suits to more comfortable uniforms.
Another enabling technology cited in the study were cluster tools, which provided optimum cycle times with relatively low tool utilization.
The study revealed that wafers in conventional stand-alone tool designs spend about 70 percent of their time waiting in line to get into the next tool chamber. When tools are integrated into a cluster, however, wafers go into a vacuum where there`s a robot to handle the wafers from one process chamber to the next, drastically reducing cycle time.
Fluor Daniel reports that in its study, cycle times were reduced from 60 or 90 days down to six. The company also reports that mini-environments and cluster tools allowed it to lower operating costs up to $4.1 million per year due to lower power costs, reduced cost of garments and reduced carrying costs.
A key financial factor among the four design options was the ability to shorten the schedule from start-of-design to production. An “over and under” design used in one of the fabs was the most successful in terms of the shortest elapsed time to production: 18 months.
The design consisted of moving some of the production into the basement to reduce building footprint and overall construction costs. This earlier production start gave it a four-month advantage over the conventional Class 1 ballroom case.
The quicker time-to-market also gave the design a four-month lead in ramp-up and learning and better prices for its new 0.35-micron products. In addition, volume manufacturing at higher prices produced higher revenues earlier than all other cases, allowing it to recover its capital spending in 10 months.
Castrucci says the study was unique because it involved a consortium of 23 companies covering all aspects of semiconductor fabrication including materials, equipment, architecture and design. “We got to hear from each one of them about what they were working on for the future. We looked at the whole picture and didn`t limit our analysis to one aspect of building a fab.”
The study simulated the development of the four fabs using a standard 0.35-micron design. Each simulated fab included process technology and a tool list, simulated fab operations, tool layouts, facility designs for the alternative fabs, cost estimates, wafer processing costs and an investment cost analysis.
Fluor Daniel believes this study has identified several inevitable trends in IC fab design and construction. A four-page executive summary and more detailed analysis of the “Strategic Fab of the Future” study are now available from David Schaefer Public Relations at (802) 864-3131, fax (802) 860-1390. n