Installing IBM Semiconductor Process Tools at Sandia National Labs

Installing IBM Semiconductor Process Tools at Sandia National Labs

In 1992, IBM offered to give Sandia National Laboratories (Albuquerque) 11 process tools that were then being used for the fabrication of semiconductor devices at its T. J. Watson Research Center in Yorktown Heights, NY. In response, Sandia established the Center for Microelectronics Technologies (CMT) in Class 1 facilities at its Microelectronics Development Laboratory (MDL). The project was one of the largest tool or technology transfers that has ever taken place from industry to government (or vice versa), involving approximately $22 million worth of equipment.

At a kickoff meeting in December 1992, the key players in the project set the goal of removing the equipment from IBM and installing it at CMT in time to produce a working semiconductor device by the end of 1993. The partnering relationships that developed in the following months led to a real commitment to the established schedule by all members of the project team. As a result, not only was the project completed on time and an engineering success, but the engineering management process developed was awarded one of the first Sandia President's Quality Awards.

Fast-Track Engineering

The donated tools included a metallization cluster tool, a CVD system, two steppers, two scanning electron microscopes, a polisher, a wet cleaner, a coater track, and a developer track. To make room for these systems, several tools in the Sandia fate had to be relocated. The process equipment installation team included two local architect and engineering (AK) firms, Smith Engineering, which was responsible for tool relocation, and Allison Engineering, which was in charge of new tool installation. J. B. Henderson Construction, an established Albuquerque company that had worked extensively with Sandia at the MDL facility (formerly the radiation hardened integrated circuit [RHIC] facility), was selected as the on-site contractor.

Figure 1: A metallization cluster tool installed at Sandia's CMT. The gas lines are routed around the wafer-handlingcomponent to supply the individual modules.

In addition to meeting technical specifications, the contractor had to be flexible with respect to expenses and yet have controls in place to avoid unnecessary cost overruns. Henderson undertook the project on a time and materials basis, which is one of the keys to fast-track, or concurrent, engineering and construction. This approach requires fewer and less-detailed drawings than conventional projects and allows more flexibility in planning. The contractor is required to give construction estimates for each segment of the job prior to beginning the work. In this case, these estimates had to be approved by the Sandia project manager, Ed Coghlan.

In addition, meetings involving Henderson and Sandia facilities engineers and process engineers were held weekly, during which any proposed field changes were evaluated and the facilities personnel were alerted to possible cost overruns. A standardized request- for- information process ensured a 24-hour response from Sandia to problems in the field, which prevented costly delays in the installation schedule.

William Strachan of IBM's facilities engineering staff worked closely with the AEs, Ed Coghlan, and Jim Wernicke, the Sandia facility engineer representing the line organization, to set the schedule and budget for each tool. IBM also allowed personnel from Sandia and Henderson to visit the Watson Center and take

pictures of the tools in operation and provided all documentation and engineering drawings relevant to the equipment. The availability of these data enabled Henderson to do a considerable amount of prefabrication and site engineering before the tools arrived in Albuquerque, thereby minimizing the time required for the actual installation.

Installation Techniques

For applications involving hazardous gases, welding is mandated by the Uniform Fire Code and the Uniform Building Code. The orbital welding technique used in this project is a well-developed process suitable for installing highpurity tubing in ultraclean facilities. The resulting welds are consistent in quality and have a smooth inner weld bead, which prevents the entrapment of particulates while permitting unrestricted gas flows. Two microprocessor controlled Model 207 welding power supplies and five Model 107 digit-switch power supplies (both Arc Machines, Pacoima, CA) were used on this job. The older model supplies had been used to install the UHP process piping system at the MDL (RHIC) facility at Sandia in 1984.1,2

Figure 2: Piping of the main utility header supplying the sputterer. The copper lines (top) are for house nitrogen and compressed air; the stainless-steel tubing is for process gases. Isolation valves and regulators are connected with mechanical fittings, while orbital welds are used after the change in direction of the tubing.

Figure 3: Weld-test coupons cut open to expose the inner weld bead for visual inspection. Coupons are labeled by date and welder identification number.

Figure 4: Finished weld on tubing connection to the sputterer. The blue seal was used to identify a weld that had passed final leak tests.

Figure 5: Doubly contained process gas lines routed into the CVD system. All lines are clearly identified.

The Metallization Tool. Of the tools being installed, the sputterer raised the most difficulties with respect to the amount and complexity of the piping and the number and difficulty of the welds. The five cluster tool modules were installed in the center of a Class 100 area and the racks of control panels were stacked along one side of the room. The extensive piping had to be routed in such a way that any single module could be removed without affecting the others (see Figures 1 and 2).

A 1/2-in.-wide weld head was used for installing this tool because of the tight clearances, and each weld was logged and marked with the welder's identification number. Weld-test coupons were made for each change of tubing size, change in mill heat number, and change from tubing to fitting (see Figure 3). Third-party quality control was performed by Clark Analytical (Albuquerque): each weld was inspected visually to ensure that it met the criteria outlined in Sandia's high-purity gas piping specifications, which prohibit any misalignment and require full penetration. When the gas lines were completed, each was subjected to helium leak testing. All of the process piping was subjected to a gross test at 250 lb for 8 hours, and regulators were tested to the rating of the lowest-rated component

Welds were inspected visually and all gas lines were subjected to helium leak testing.

in the system for a second 8-hour period. This testing was followed by tests for trace gas and particulates and final helium leak testing at 10-8 atm cm3/sec.. All lines that passed the tests were marked with blue seals (see Figure 4).

The CVD System. Welding challenges were also presented by the CVD system. Doubly contained process gas lines from the facility's basement enter a valve box and feed into a cabinet with bulkhead fitting (see Figure 5). From there, the lines run along the ceiling and then down to a panel inside the tool. Copper tubing carries house nitrogen, which is used for initial purging; stainless-steel tubing is used for argon, oxygen, and nitrous oxide; and phosphine, silane, and ammonia are delivered in coaxial lines in compliance with the Uniform Fire Code. For these coaxial lines, the inner tubing was prepared for welding by machining the tube ends and then joined with an autogenous fusion butt weld. When the welded assemblies had been pressure tested for leaks, residual gas, and particles, a sleeve was moved into place over each joint on the outer containment tube and welded in place at both ends, as shown in Figure 6. The welded coaxial lines were then submitted to the same pressure testing procedures as the inner process tubing.

Sandia is one of the few semiconductor facilities using all-welded coaxial lines. Although the advantages of an all-welded system would seem obvious, many contractors use mechanical fittings for outer containment tubing because they feel the type of weld required is too difficult or too costly. All welded sleeves provide the capability for vacuum monitoring of individual lines, which can be linked to an automated facilities monitoring system. When the annular space between the containment and process lines is held at a static vacuum of 50 µm, it is possible to detect and discriminate between leaks in the process lines and leaks in the containment lines. This is not possible when mechanical connections are used, because their fittings will not hold a vacuum at the desired level for long periods of time.

Prefabrication Welding. It is always advisable in a cleanroom installation such as this project to prefabricate as much of the system as possible and to keep the number of field welds, which can cause system contamination, to a minimum.

With all-welded sleeves, it is possible to detect leaks in both process and containment lines.

Sandia provided Henderson Construction with a portable Class 100 cleanroom in the basement of the MDL facility for this purpose. One welding power supply was placed inside the cleanroom, while a second supply was stationed directly outside it (see Figure 7).

During the project, an average of five teams consisting of a welder and a fitter were at work at the same time. Two welding technicians might be in the portable cleanroom fabricating spool pieces, for example, while a field crew installed the preassembled pieces. All team members were required to wear cleanroom apparel in the cleanroom and to be gloved at all times, in or out of the cleanroom.

Other Considerations. Some extra effort on the part of the contractor and the welding equipment supplier was required to achieve compliance with Sandia's specifications, which did not permit any misalignment of welded components. The welding teams created special tools for aligning tubing with the tungsten electrode in the weld heads and used a modified vise grip to hold tubes in place during welding. Working with the customer, the equipment supplier designed a special tube-clamp insert to provide better tube alignment in the weld head.

Figure 6: A sleeve welded to the outer coaxial tubing for the transport of hazardous gases to the CVD system. A termination fitting is shown in the foreground.

Figure 7: Welder in cleanroom apparel at orbital welding station just outside the basement cleanroom at Sandia.

Maintaining control of incoming materials was also essential to good weldability, particularly for the containment tubing sleeve welds. Mismatches in sulfur content, especially between tubing and fittings where arc deflection can occur, had caused problems on previous Sandia installations. For this project, the sulfur contents on 1/4- to 2-in.OD and 2- to 4-in.-OD tubing were held to between 0.005 and 0.012% and 0.005 and 0.017%, respectively. Tubing extensions on valves were controlled to similar levels.

In comparison, the ASTM/ANSI specification for 316L stainless steel permits sulfur contents of O.001 to 0.030%. Sandia is presently keeping material in stock in order to ensure a good match in the sulfur contents of tubing, sleeves, and other fittings.

Testing of the installed gas lines indicated that all specifications were met or exceeded. Contaminants were measured at <10 O.1-µm particles/std cu ft, with no particles >0.5 µm. Total hydrocarbon content and residual moisture and oxygen levels were found acceptable, with no single impurity increased by more than 100 ppb over the level present in the source gas.

Conclusion

Successful partnering depends on early identification of the key players and the establishment of guidelines

defining their roles and responsibilities. During the course of this project, weekly progress meetings were held to maintain a constant avenue of communication and to provide a conflict resolution matrix, which enabled any problems or potential problems to be addressed immediately. Preplanning and site visits to IBM were also critical to the project's success, as was the use of orbital welding for both single and coaxial process gas lines.

All of the IBM tools installed at Sandia were operational by the December 1993 target date, and since then the MDL center has established several collaborations with private companies in which the equipment is used to demonstrate the efficiency of new tools and processes and to foster the development of new technologies.

Acknowledgment

Work on this project was supported by the United States Department of Energy on Contract No. DE-AC0494AL85000.

By Barbara K. Henon, Ph.D., Arc Machines, Inc., and Ed Coghlan

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