Realizing the 450mm transition
10/01/2008
EXECUTIVE OVERVIEW
The International SEMATECH Manufacturing Initiative (ISMI) is actively involved in building the foundational infrastructure and coordination of activities to enable a 2012 pilot line target date at the direction of its members. To realize this goal, ISMI is coordinating and facilitating activities related to silicon, guidelines, standards, EHS, equipment development and operations.
ISMI initiated a program in 2008 solely dedicated to enabling a cost-effective 450mm transition through coordination and development of infrastructure, guidance, and industry readiness. Development and testing of 450mm silicon wafers is one of several key focus areas to enable cost-effective development of hardware. Refining guidelines developed by consortia members and working with SEMI standards task forces takes priority. Testing of prototype factory interface components is also a major focus to enable data-based decisions on development directions and standards development. Areas such as EHS and economic monitoring while continuing to facilitate dialogs with individual suppliers, SEMI, and the greater industry are also critical to the program’s success. Enabling a 450mm pilot line in the 2012 timeframe is the goal.
Silicon readiness
The first type of silicon required for 450mm hardware development is a mechanical handling wafer to test shipping carriers (FOSB), in-fab carriers (FOUPS) and robot handling systems for AMHS/production equipment interfaces. The mechanical handling wafer is also used to make early measurements of the wafers’ physical properties, with gravitational sag being the parameter of most concern to the carrier and robotics development. Sintered polysilicon wafers were a breakthrough in providing cost-effective wafers that mimic the mechanical parameters of single crystal silicon.
Tests comparing single crystal with polysilicon show nearly identical results, proving the utility of this cost-effective solution. These wafers have been commercially available since mid-2007 from Nikko Metals and Mining. ISMI has purchased five different thickness, both thicker and thinner than 925µm, to evaluate sag and other mechanical properties. The desire is to find the thinnest feasible to maximize the number of wafers obtained from a single crystal-grown boule. But the wafers must also be thick enough for reliable use in IC fabrication processes. ISMI is working closely with the SEMI Mechanical Handling Wafer Task Force and will continue engagement in the single crystal era.
ISMI purchased 100 of these polysilicon wafers for internal testing (Fig. 1). The bulk of the wafers are 925µm thick conforming to the provisional value. ISMI created a silicon bank where wafers are loaned to suppliers for testing at their locations. At the time of writing, the silicon bank had made over 11 loans totaling over 70 wafers.
 Figure 1. ISMI assignee Mike Goldstein holding a 450mm sintered polysilicon wafer. |
null
Guideline clarification
The 450mm Guidelines and Standards project at ISMI is geared towards providing clarifications and refinements to the 450mm specific 19-point guidelines issued by ISMI in 2007. This work is currently focused on clarifications for carrier design, wafer handling, and material handling. Backside contact area clarifications for wafer handling and carrier contact have been provided for discussion to understand tradeoffs. Another area is manual handling design aspects for the larger, heavier carrier. Wafer pitch within the carriers is a major item of attention with the 10mm pitch expectation, but other areas of interest are being investigated such as carrier ID, carrier vibration, and future requirements for purging of carriers with inert atmospheres. This group is working closely with the SEMI IPIC (physical interfaces and carriers) Task Force providing inputs and taking requests for action.
Interoperability test bed (ITB)
The collection of hard data on prototype hardware and components is a major endeavor of the 450mm program. The intent is to identify challenges and provide data on wafer handling approaches to avoid historical non-data driven guideline and standards decisions. ISMI has set up a testing facility in the lab space adjacent to the former SEMATECH cleanroom (ATDF) in Austin, Texas. At the time of writing, a prototype carrier with 10mm pitch from Entegris and a robotic test stand from Brooks had cycled over 100k passes including polysilicon mechanical wafers (Fig. 2).
 Figure 2. 450mm wafer cycling at ISMI’s Interoperability Test Bed (ITB) in Austin using an Entegris prototype carrier at 10mm pitch and a Brooks prototype robot. |
Additional carrier hardware from another supplier is en route and additional contract discussions are underway. Physical measurements are being made with coordinate measurement metrology (CMM) acquired from Hexagon in the Austin lab. Various wafer carrier, robotics, and AMHS suppliers are participating in ISMI’s Test Bed User’s Group to work together for better communication and understanding towards interoperability testing. ISMI has also agreed to work with the interoperability test bed???Japan (ITG-J) to work in a complementary way to provide data to the standards processes. The ITG-J is a collection of Japanese AHMS, wafer handling, and carrier suppliers with a similar mission as ISMI’s ITB.
Industry engagement
The overall program has been working to coordinate these activitities and to work with the industry at large. ISMI will continue to engage with the industry at major forums and with the SEMI community. The 450mm program has also engaged with over 20 fab equipment suppliers to provide better understanding of ISMI’s program, understand suppliers concerns and determine what ISMI can do to assist in cost-effective development of 450mm equipment. Many suppliers were found to have formed 450mm task forces and some have developed sophisticated feasibility studies for 450mm equipment. Suppliers were also interested in the ability of ISMI to provide test wafer generation and metrology capability. Even proposals of 450mm equipment for ISMI have been received.
Environmental, health and safety (EHS) challenges for 450mm equipment factories are being assessed this year and additional study is planned for 2009. ISMI is also holding to its charter of constantly monitoring the industry economics for better understanding and decision making. Finally, this program is involved in several industry collaborations and coordination activities at the industry level for better understanding and cooperation.
Future plans
ISMI plans to expand its activities in 2009. Single crystal process test grade wafer definition, testing, and availability will be one challenge. It is expected that early single crystal wafers will be acquired by the end of 2008. Working methodically toward definition and availability of production grade wafers is the long range plan.
Expanding the scope of the ITB activities will be another major area for 2009 with additional hardware, more sophisticated hardware, and interoperability testing. This includes continued interaction and data sharing with the standards task forces. The EHS activities will expand considering the mounting interest in green manufacturing, safe handling of carriers, and hardware among other concerns.
The 450mm project poses a number of operational challenges to be investigated for factory operations for various business models from the time wafers arrive at the dock until the wafers are diced. Engagement with fab equipment and metrology suppliers will expand to enable 450mm development including evolving business issues, equipment performance metrics, and test-wafer generation and metrology support.
Strategic planning for enabling a 2012 pilot line target includes multiple components such as robust factory integration standards, guidance on equipment and factory aspects, test-wafer generation and metrology support, equipment demonstration guidance, and the continuous improvement of silicon toward device-grade silicon.
Conclusion
ISMI’s 450mm program has been pursuing the realization of a cost-effective wafer size transition to 450mm. Building enabling infrastructure involves the development of cost-effective wafer using cheaper polysilicon in the initial stages and provides learning to the suppliers of single crystal silicon. Another aspect is the development and communication of guidance to the industry on 450mm and future factory requirements including close interaction with SEMI Standards task forces. Significant efforts have been applied to the creation of a factory interface test bed where early learning can benefit industry direction. Early engagement with the industry and suppliers has been a lesson learned from 300mm and a focus of the 450mm program, along with analysis of ESH challenges and the drive towards green manufacturing. ISMI will be working methodically to advance the needed building blocks to enable a 2012 pilot line target.
Cost-effective and efficient use of industry resources are key guiding factors in the realization of 450mm. ISMI is dedicated to coordinating and facilitating the necessary activities related to silicon, guidelines, standards, EHS, and equipment development and operations. ??
Tom Abell received his BS and MS from Purdue U. and is the 450mm program manager at International SEMATECH Manufacturing Initiative, 2706 Montopolis Drive, Austin, TX 78741 USA; ph.: (512) 356-7441; email [email protected].