Test Automation in the 300 mm Environment

		At a Glance
	The move to 300 mm wafer sizes presents special challenges to the test community, most in the area of wafer handling. Pertinent standards are reviewed, and solutions are suggested.

Implementing 300 mm factory automation standards is a key topic among most semiconductor industry managers and executives faced with bringing 300 mm fab capacity on-line. Implementing these standards in parametric and wafer sort test cells presents special challenges with respect to wafer movement, handling and identification, along with process recipe control. This is largely because the materials movement function and the materials processing function are divided between two separate tools: the test system and the prober.

Both inline parametric and wafer sort test processes are included in the vision of what a fully automated 300 mm fab would look like. To achieve the published target economics and production productivity for 300 mm, all material transport into and out of the test cell -- as well as test process execution -- must be automated. The 300 mm fab will be optimized for this automation, not operators, and will require highly integrated host computer-integrated management (CIM) systems. The test cell must support this required level of automation.

A brief history

The move to 300 mm wafer capacity is being driven by leading foundries in an attempt to obtain a competitive advantage. Unlike the transition to 150 mm in 1984 and 200 mm in 1992, however, the move to 300 mm wafer capacity includes a significant industrywide effort to define factory automation standards and process performance improvement goals. A comprehensive set of guidelines titled "Global Joint Guidance on 300 mm Semiconductor Factories" was released jointly by the I300I (International 300 Initiative) and J300 (Japan 300 mm Conference) consortiums at SEMICON West in 1997. The I300I comprises 13 companies (three European, three Korean, one Taiwanese and six U.S.). J300 is the Japanese equivalent of the I300I.

Major expected performance targets include 5-10% lower cycle times, 10-20% greater tool utilization, and 5-10% yield improvement compared with current 200 mm fabs. Overall initial 300 mm factory operation costs related to wafers must be reduced by a minimum of 25%, with reduction targets in the range of 30-40%. In addition, productivity increases of 30% are needed.

Using the GEM interface solution, the test system can appear as a virtual GEM host to the prober and a virtual prober to the factory host. The factory sees a single communications port.

By defining common objectives for tool performance from the outset, greater tool supplier and user participation is ensured, as is stricter adherence to equipment standards.

Cooperation among Semiconductor Equipment and Materials International (SEMI), International SEMATECH, and the I300I and J300 consortiums has resulted in considerable progress being made in equipment standardization and process automation. The mission of I300I and J300 has been to manage equipment and factory development and automation issues resulting from a change in wafer size. SEMI and SEMATECH have provided significant technical support and guidance, along with standards development, to support the consortium's efforts.

The first implementation of the initiative's goal was realized in January 2000 with the completion of Semiconductor300, a joint pilot partnership between Infineon Technologies and Motorola in Dresden, Germany. Since then, 48% of all new fab starts in 2000 have been 300 mm. Growth of 300 mm is expected to continue in 2001, with construction beginning on at least eight new fabs. It is expected that, in 2002, there will be more 300 mm than 200 mm capacity coming on-line.

Understanding the specifications

To provide guidance and enable all of the required automation in materials movement, delivery, tracking and processing, SEMATECH has authored Technology Transfer Document #97063311G-ENG, I300I Factory Guidelines: Version 5. This document provides a comprehensive overview of all relevant SEMI and ISO standards, as well as related SEMATECH documentation. Of the 52 standards noted by SEMATECH, only 10 are relevant to CIM automation of the test cell in the 300 mm environment. They can be grouped as shown in the Table.

Factory Automation Standards
Category	Standard	Application
Protocol and communication	SEMI E5 (SECSII) SEMI E37/37.1/37.2	Message content High-speed SECS message service (HSMS)
Tool behavior	SEMI E30 (GEM) SEMI E30.3 (TSEM) SEMI E91 (SEM)	Generic model for communications and control of SEMI equipment Testing equipment specific model Prober equipment specific model
Materials movement	SEMI E87/87.1 SEMI E90	Specification for carrier transfer standard Specification for substrate tracking
Data and process recipe control	SEMI E39 SEMI E40 SEMI E42 SEMI E94	Object services standard: concepts, behavior and services Standard for process management Recipe management standard: concepts, behavior and message services Standard for control job management

It is important to note that the SEMATECH document does not specifically identify SEMI Specific Equipment Model standards E30.3 (TSEM) and E91 (PSEM). These standards have been added here because they apply to the specific case of automating test cells.

Overall, 300 mm requirements can be viewed as building upon both traditional tool communications and the behavioral foundation of SECS/GEM (defined by the SEMI E5/30/37 standards). Added to this foundation is wafer carrier and tool port management via the carrier management standard (SEMI E87), and the substrate tracking standard (SEMI E90).

Data objects are standardized in the object services standard (SEMI E39). Finally, the determination and assignment of the correct processing job and process recipe to the wafer are covered in the job and process control standards (SEMI E40/42/94).

Test cell automation challenges

We can generally classify the job of any given process cell into two functions: materials movement and materials process. The materials movement function is concerned with the physical location and identification of the wafer material. The materials process function is concerned with the physical processing that will be performed by that cell.

As a simple example, consider a very generalized description of an ion implanter. The materials movement function detects the arrival of wafers at one of its input ports in a cassette contained in a front-opening unified pod (FOUP). The wafers are moved from the wafer cassette inside the FOUP into the implant chamber. The processing function then takes over and the implant occurs. Next, the materials movement function moves the material out of the chamber and into the appropriate cassette inside a FOUP at another port. Applying these classifications to a test cell is easier to visualize. In a test cell, two separate tools accomplish the functions. The test system assumes responsibility for the process function. The prober, connected to a FOUP port handler, assumes responsibility for the materials movement function.

From the perspective of the CIM host system, a test cell is just another process tool cell that the material must flow through. Using the appropriate GEM-based SEMI standards, the CIM host system will deliver wafer material to the process cell through a variety of material systems such as overhead tracks (OHTs), personally guided vehicles (PGVs) and remotely guided vehicles (RGVs). The process tool cell can accept the FOUP from the delivery system at a single port, or at any one of the ports in the case of a multiport tool. The CIM system will also have to identify and deliver the correct process job and process recipe information for the material currently loaded into the process function of the cell.

It is the responsibility of the process tool cell to report the exact status of the material back to the host via the appropriate GEM-based SEMI standards. This status includes the material currently under process, as well as the availability of new material at any input port or output port. The process cell will need to provide the CIM system with information to enable single-wafer tracking and identification by cassette and slot in the FOUP, as well as the status of the FOUP port. The CIM system cannot be burdened with determining if the report is from the materials movement function or if it is from the materials processing function, or if separate tools perform these functions.

The tool cell is therefore responsible for all local states and events regarding both the material and equipment, and for reporting this information back to the hosts, as required by the host, without impacting throughput.

To meet the above requirement, the CIM system should view the process tool cell as a single point of communication. Likewise, the tool cell should behave as a single integrated materials movement and processing function. In the framework of a GEM scenario, the single point of communication would physically be a single HSMS communications port.

In implementing this level of automation for a test cell, the developer must first account for the fact that, to accomplish the required materials movement and processing functions, the test cell requires a minimum of two totally separate and critically important tools, which are provided by different companies. The prober performs the materials movement function, while the tester performs the materials processing function. Further complicating this setup is the fact that the 300 mm test cell now also includes the FOUP handler. In this context, it is possible that the test cell could have three individual connections to the CIM system, governed by at least 10 different SEMI standards. In addition, at least three process state models are in effect at any given time: the tester process state model as defined by SEMI E30.3, the prober equipment state model as defined by SEMI E91, and the FOUP port state model as defined by SEMI E87. This clearly violates the requirement that the CIM system view the cell from a single communications point.

Addressing the challenge

The solution for aggregating the three separate tools and 10 relevant standards into a single-point/single-wire interface is to allow the test system to act as the message arbitrator for the host. By establishing the test system as the arbitrator between the host and the test cell, the test cell satisfies the CIM needs of the host. The test system controller can forward material movement commands and data to the prober, while also collecting commands and data from the FOUP and prober.

Accomplishing this in the SEMI standard GEM environment can prove problematic because GEM is a point-to-point communications protocol. Point-to-point means that the tester must talk directly to the GEM host, the prober must talk directly to the GEM host, and the FOUP must talk directly to the GEM host. Unfortunately, there is no definition for an arbiter function in the communication between a tool and a factory GEM host. Also, there is no generally accepted guidance for managing the three process state models.

To address these issues, a 300 mm GEM interface solution has been developed. In this solution, the GEM interface layer is abstracted from the hardware layer, and exists as a separate software process on the test system controller. Using a distributed messaging system, the tester controller can appear as a virtual GEM host to the prober, accepting all of the relevant materials movement functions. Likewise, this GEM interface can appear as a virtual prober to the actual factory GEM host, and pass on the relevant prober communications.

The net effect of this design is that, in the factory-to-tool communications direction, the factory does, in fact, see one single communications port. It sends all materials movement function and materials process function commands to the single port, and the GEM interface determines if the information is relevant to the tester or the prober. Prober-relevant information is repackaged as a GEM command and sent to the prober. In the tool-to-factory communications direction, it appears to the prober as if it were, in fact, communicating directly with the factory. The interface receives the GEM communications from the prober, aggregates it with the relevant tester information and sends a repackaged GEM function to the host.

Benefits to 200 mm

As companies transition to 300 mm, they are discovering that automation processes can also benefit 200 mm environments. The 200 mm manufacturing processes can bring up the same CIM operational infrastructure as their 300 mm test processes under construction. While some of the automated materials movement functions would not be practical, several other components of 300 mm automation  such as reduced operator reliance and more accurate, effective recipe downloads and equipment management  can be beneficial. In this environment, bridge equipment, which can handle 200 mm wafers and then be upgraded to handle 300 mm wafers, may help alleviate some of the strains of converting to 300 mm.

In Agilent Technologies test systems, the GEM interface capabilities have been designed to be scalable from a 200 to 300 mm environment. The 200 mm version of the GEM interface solution product is available on most test platforms. The 300 mm single-wire interface will be available on all Agilent semiconductor test platforms in the second half of 2001. The single-wire 300 mm GEM interface solution addresses the complete cell solution of FOUP, prober and tester.

Denise Jenkins, technical agenda program manager for Agilent Technologies' Automated Test Group, has more than 12 years' experience in the areas of semiconductor product, test, design and applications engineering. She has a BSEE and an MSEE from Northeastern University (Boston) and an MBA from Santa Clara University (Santa Clara, Calif.).

William O'Grady, program manager for Agilent Technologies' GEM Factory Automation Program, has worked in the industry since 1983 and previously held positions at Fairchild Semiconductor and Hewlett-Packard. He has a BSEE from the Rochester Institute of Technology (Rochester, N.Y.) and an MBA from the State University of New York at Albany.
Phone: 1-512-257-5827
e-mail: bill_ogrady@agilent.com