Two SEMI groups discuss 9-in. reticle carriers

05/01/1998

Two Semi groups discuss 9-in. reticle carriers

As the maskmaking industry works to implement standards for the transition to 9-in. reticles, two SEMI task forces charged with designing carriers for the larger glass substrates have taken divergent paths on their box designs. The North American group is placing minienvironments at the core of its design, while the Japanese group is opting for optimized containers for specific functions. As a result, four very different carriers are now being proposed for adoption. "We`re working under different assumptions, so we`re coming to different conclusions," said Bob Davis, co-chair of the SEMI North America reticle carrier task force and PRI Automation`s product manager for lithography systems automation. "None of their three carriers look like our carrier," he said. "There`s a likelihood that the industry will adopt all four."

The SEMI NA task force`s proposal, a single unified pod for all applications, is based on a minienvironment infrastructure, and on the idea that automation will be critical in the transport of the larger reticles.

Moreover, the SEMI NA proposal has taken an inter-operable approach to its design. The reticle-FOUP (front-opening unified pod) is based on the 300-mm wafer FOUP with the same kinematic couplings, box clamping features and optional automation handle. It can also be used for 6-in. reticles; it includes purge ports, exclusion zones, and other features.

In short, the proposal offers a guideline for the exterior of the box and interior spaces. But, in contrast to the current SEMI Japan proposals, the SEMI NA proposal does not specify interior mechanisms for any particular application. "You can`t make a product from the North America guideline," Davis said, noting that a carrier manufacturer would use the guideline to design the carrier shell, adding interior mechanisms for specific applications. Davis added that a "clever" box designer could conceivably find one interior design for all applications.

The SEMI Japan task force, however, has come up with three proposals - a shipping box, a mask shop box, and a box for use in the fab. Toshiba`s Iwao Higashikawa, co-chair of the SEMI Japan task force, said the proposals are based on optimizing the carrier for each process step. "In the beginning, we tried to make clear the needs for the carrier on each of the process steps," Higashikawa said. "Our approach was to first draw each carrier and when similar, they join into one idea. To minimize cost, (this approach) seems to be better."

One issue is reticle storage inside stepper enclosures - the Japan group contends that a minienvironment scheme would result in boxes being too bulky to be accommodated in large numbers. The group also cites special needs of maskmaking lines, which handle resist-coated substrates, and a desire for better clamping capabilities in a shipping box. But Davis points out that there are "inherent costs" of having three carriers instead of one.

The move to 9-in. reticles - driven by the move to scanning lithography, larger die sizes, and the need for multidie reticles - is starting this year, and will stretch out over the next four years, according to a Grenon Consulting survey presented at SEMICON Japan in December.

Davis said the first major review of the standards is planned for SEMICON West in July, but work will continue throughout the spring to review and revise the two task forces` proposals.

Higashikawa said his team would like to see more detailed drawings about the SEMI NA proposal`s interior spaces, which he said are currently too narrow. "It seems impossible to make enough holding parts in it," he said. Work is underway to come up with a minienvironment carrier similar to the SEMI NA FOUP for use in the stepper. "SEMI Japan is discussing specific designs for stepper carriers now, and next we are going to propose simple guidelines on the exterior, interior, and interface. At that time we would like to unify as much as possible to the NA proposal." - C.L.