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August 2007

Automating silicon crystalgrowth earns Howard Zinschlag Sperry Award

By Jim Strothman

“Until my project team and I successfully automated the growth process, it was controlled manually by crystal puller operators. Since the growth process was sometimes 40+ hours long, there were many chances for operator error, which resulted in worthless crystals. With the DADC control system, enormous cost savings and yield improvements were realized.” —Zinschlag

Perhaps no single material has been more critical to the computer industry—and representative of the spiraling downward price/performance costs which continuously fueled the computer industry’s success—than silicon.

So in 1979, when digital computers were still beginning to find niches in the industrial and business worlds, semiconductor manufacturers everywhere were demanding high-quality silicon wafers.

Monsanto Company, a pioneering computer technology developer, was seeking to be a major supplier of silicon wafers. However, a faltering Batch Czochralski (BCz) crystal silicon growth computer automation project the Monsanto Electronic Materials Company (MEMC) had been working on for five years still was not successful. 

J. Robert Middleton, a Monsanto central engineering director, who a year later served as ISA’s 1980 President, transferred a talented electrical and computer engineer, Howard P. Zinschlag, P.E., to MEMC’s St. Peters Plant headquarters in Missouri, designating him team leader in charge of fixing the problem. 

“As a result of my investigation, I stopped the project and redirected the effort to a more technically sound concept,” said Zinschlag. “I prepared and issued a much needed Functional Systems Specification and committed to a very ambitious development schedule, which was completed on schedule. The batch process required tight control of eight analog variables and discrete functions for a total ingot growth time of 40+ hours.”

The pioneering work resulted in MEMC becoming a world class supplier of silicon wafers to IBM, Intel, Texas Instruments, and other semiconductor industry giants. The design was successfully installed and started up at all the company’s silicon manufacturing plants worldwide, including in Italy, Korea, Taiwan, Japan, and two U.S. plants.

That success—combined with other significant engineering and technical management feats, including pioneering computer memory systems—resulted in Zinschlag being honored this year with ISA’s Albert F. Sperry Founder Award – ISA’s outstanding achievement award. 

“The Albert F. Sperry Founder Award will be awarded to Howard P. Zinschlag for outstanding technical contributions and leadership in the silicon industry and, in particular, for his pioneering computer automation of silicon crystal pullers for the growth of single crystal silicon ingots for the semiconductor industry,” said Henry Hegner, chair of ISA’s Sperry Award committee.

The honor recognizes “an outstanding technical, educational, or philosophical contribution to the science and technology of instrumentation, systems, and automation.” It is named for Albert F. Sperry, who was internationally recognized for his contributions to the advancement and development of instrumentation as an innovator, business executive, and ISA leader. Sperry served as the first ISA president in 1946 and was elected an Honorary Member of ISA in 1956. 

“I was honored and humbled by being both nominated by 2002 ISA President Pino Zani for—and then receiving—the prestigious Albert F. Sperry Founder Award by the 2007 Honor and Awards Committee, my ISA peers, and therefore to be now counted among the previous distinguished recipients of the award,” said Zinschlag, who just turned 70 years old.
 
The award may be conferred annually and carries a $3,000 honorarium and plaque. Zinschlag will be recognized for receiving it at ISA’s annual Honors and Awards Gala in Houston on 1 October.

Silicon ingot process explained

Phase 1 of the process to grow a single crystal oriented silicon ingot begins with the meltdown of a poly silicon raw material (having no definitive crystal orientation) using a 30 kilogram charge at 1,425 degrees centigrade in a large vacuum system called a crystal puller, said the Sperry Award winner. Ingot growth is started by dipping into the molten silicon charge a 3-millimeter (mm)-diameter silicon crystal “seed” with a known and desired crystal orientation. 

As the “seed” is slowly withdrawn from the silicon melt, a silicon “taper” is grown that is the continuation of the crystal “seed” and that assumes the same crystal orientation as the “seed” crystal. By precise control of temperature, pull rate, crucible rotation (the vessel that holds the molten silicon charge), “seed” and ingot rotation, shape of the meniscus of grown ingot at the melt surface, diameter, power, and growth surface position of the molten silicon charge, and other discrete controls, the 3mm “seed” crystal is grown to the desired silicon ingot diameter—100mm to 300mm. 

When the correct diameter is obtained, the silicon ingot growth enters Phase 2. By controlling the eight analog variables listed and other discrete functions, the diameter growth of the ingot is maintained, and the ingot is grown to very tight diameter tolerances to a length of more than 36 inches. An “under diameter” crystal is worth nothing, and an “over diameter” crystal wastes silicon material. When the molten silicon charge is finally almost depleted, the growth of the crystal ingot enters Phase 3.

In Phase 3, the crystal growth is terminated by growing a “tail” with similar characteristics as the growth of the “seed taper” in Phase 1. If at any time during the 40+ hours of ingot growth the control parameters are not maintained to within tight specification limits, the silicon ingot single crystal orientation is lost and the ingot becomes worthless.

Considered an ‘industry first’

“In less than two years, my project team and I successfully demonstrated a Digital Automation Diameter Control (DADC) system that automated the silicon growth from “seed-to-tail,” Zinschlag said. “This successful automation of the BCz silicon ingot growth was believed to have been the first in the industry and was considered to be the best computer control system for ingot growth in the industry for many years thereafter.

“Until my project team and I successfully automated the growth process, it was controlled manually by crystal puller operators,” he said. “Since the growth process was sometimes 40+ hours long, there were many chances for operator error, which resulted in worthless crystals. With the DADC control system, enormous cost savings and yield improvements were realized.” After the achievement, Monsanto decided to hold the work “Company Confidential” and not pursue patents in order to prevent the loss of MEMC’s competitive cost advantage achieved with the project. 

“While it is hard to quantify the exact amount of revenue that this work produced for the company, the original project premise was conservatively based on a 10% savings per crystal ingot,” Zinschlag said. “However, subsequent additions and improvements to the system resulted in annualized throughput improvements of 20%, yield improvements of 15%, and manpower savings of 20%. As many crystal pullers were run 24 hours a day, 7 days a week, many ingots were grown over the 15 years the developed system was used before it was finally retired and replaced with the next generation control system,” he said. 

“As a result, this development work produced significant annual cost savings for the company for those 15 years,” Zinschlag said.

Previous engineering successes

Zinschlag—who left a Silicon Valley company he helped found, Fairchild Memory Products Co., to join Monsanto in 1968—had previously distinguished himself in 1969 in a project also managed by Middleton, attempting to design and develop a unique platform to computerize process industries. The team successfully created a computer system designed specifically for process control. When coupled with the very first cathode ray tube display, it provided the breakthrough needed for the world of direct digital control of processes.

“While I was primarily responsible for the management of the hardware design and development of the Digital Control Computer (dc2), I was able to bring my past computer memory design experience to the project and personally developed the memory subsystems for the computer, both the read-write and read-only memory systems,” Zinschlag said. “Of significant importance was the development of the read-only memory system which allowed for the first time in industry to have the process control firmware hardwired into the computer.”

The dc2 was initially used to automate petro-chemical processes at Monsanto plants exclusively. In 1971, however, Fisher Controls of Marshalltown, Iowa, a Monsanto subsidiary, introduced the dc2 computer-based digital control center to the marketplace. Complemented by the pc2, process control center, the new digital system significantly improved distributed data control and supervisory control, plus batch sequencing. 

“Many other instrument and control companies followed quickly with like systems, and the world of direct digital control for process and power plants was born,” Zinschlag recalled.

Significantly cut downtime

As a follow up to the silicon wafer process work begun in 1979, and with direction from MEMC’s Dr. John P. De Luca, VP Technology, Zinschlag and a group of scientists worked on developing a Continuous Czochralski (CCz) crystal growth process. In the earlier BCz process, only one crystal ingot is grown per setup of the crystal growth furnace. After the batch of molten silicon is depleted, the furnace is cooled, cleaned, and recharged with more silicon material and the growth process restarted, which “significantly impacts throughput, material costs, and manpower expenditures,” Zinschlag said. 

“It was demonstrated that it was possible to grow multiple crystal ingots from a single furnace setup by continuously recharging the molten silicon charge in real time while the ingot growth process was being executed. This was a very complex problem of crystal growth and system control/automation to solve in order to produce multiple high quality ingots during a single ‘run.’

“After several years of intense work, a CCz process was demonstrated where up to five crystal ingots were grown successfully without requiring the shutdown of the growth furnace for sometimes up to four days. To the best of MEMC’s knowledge, this had never before been accomplished. This monumental effort by my group required all of their combined technical expertise and close technical management and coordination,” the Sperry Award winner said.

 Developed memory systems

After graduating from the University of Illinois in 1959 as an electrical engineer, Zinschlag went directly into R&D at the Philco-Ford Development Center in Willow Grove, Pa. He was assigned to a group chartered to design and develop one of the first all-solid-state military computers using a magnetic core memory system.

Later, following an honorable discharge from the U.S. Air Force, he joined Fairchild Semiconductor laboratories in Palo Alto, Calif., then run by industry giants Robert Noyce and Gordon Moore (of Moore’s Law fame), who together later founded Intel. Moore and Noyce gave Zinschlag’s boss funding to “buy a building, hire people, and start a memory company,” which became Fairchild Memory Products Co. “I had the chore of training the first person, in addition to designing the first memory system product,” Zinschlag recalled.

After returning to MEMC, Zinschlag automated other silicon wafer processes and introduced more state-of-the-art technology to the silicon materials industry. They included the use of voice recognition systems in the manufacturing process; vision control systems for process control; and laser devices for marking silicon wafers for identification, material tracking, and certification.

Led ‘Technical Renewal’

In 1996, Zinschlag was promoted to Technology director, reporting to Dr. De Luca, VP Technology of MEMC. He was asked to spearhead a Technical Community Renewal program within MEMC, which required direct coordination of all world area technology facilities and programs to assure technology information was shared and transferred in a timely fashion and duplication of research at different sites was not occurring. The bottom line was to bring synergy to MEMC’s worldwide technology work. 

“The communication and leadership skills that I acquired through my involvement and participation in ISA helped me meet the challenges of this tough assignment. The program was very successful, and MEMC benefited from the work,” he said. 

Zinschlag retired from MEMC as Technology director in 1998 and currently does some consulting work.

ISA accomplishments

Zinschlag joined ISA in 1974, prodded by Robert Middleton, who later became an ISA President. “His first assignment to me was to write and deliver a technical paper at the next ISA Conference and Exhibit based on my experiences in the semiconductor industry in Silicon Valley,” the Sperry winner recalled. “I co-authored a paper entitled, The Microprocessor Impact on Process Control Systems.”

The paper predicted in 1975 the impact that microprocessor technology would have on the computing industry and, more specifically, the impact on the process control industry regarding distributive control, smart transmitters, communication between field control devices, and self checking, among other advances. 

“By the end of the 20th century, many of these predictions had already come to pass and are still being introduced today,” Zinschlag said.

“Again, by the urging of Bob Middleton, I joined (ISA’s) Data Handling and Computation Division. Immediately it became apparent to me that the division was not serving the present day needs of their division membership. In 1978, I reorganized the division and founded the current day Computer Technology Division. This change in division scope started to bring computer professionals into the society.”

Zinschlag was elected an ISA Fellow in 1986, and, in 1992-93, served as ISA President. His presidential theme was “Remember the Member,” and his focus was on “Change, Challenge, and Opportunity.”

“My passion for more than 20 of my 33 years with ISA has been the globalization of the society. When I was president, I had the opportunity to travel the world to promote the engineering fields of instrumentation, systems, and automation to practitioners of engineering and students studying engineering in some European countries, including Ireland, and also in Russia, India, China, Turkey, Korea, Brazil, and Mexico, he said. 

He later chaired ISA’s International Development Council and Globalization Committee, and recently served on ISA’s Finance and Investment Committees and special Task Forces.  “Now, as we are well into the 21st century in ISA, I can see the results of that early work coming to pass. It is very gratifying to me to see the direction that ISA is going in furthering globalization and learning how to marry and integrate different cultures and nationalities into the ISA family.” He was nominated for the Albert F. Sperry Founder Award by another former ISA President, Piergiuseppe (Pino) Zani, and received written endorsements from former ISA President Middleton and retired MEMC Corporate VP Technology De Luca.  

Now semi-retired, Zinschlag continues to do some technical consulting. A registered professional engineer, he is a graduate of the University of Illinois (’59 BSEE), Santa Clara University (’66 MSEE and post graduate studies), a 1986 ISA Fellow, and a 2005 University of Illinois Distinguished Electrical and Computer Engineering Alumni.

In addition to his wife and Middleton, Zinschlag credits former ISA Executive Director Glenn Harvey for being “a great sounding board who offered help and guidance to me through my ISA years.”

“I appreciate the opportunity to be able to give back to my automation profession just a little of what it gave to me. For 33 years, ISA was one primary conduit for that feedback to the automation profession. I have always believed that it was very important to volunteer one’s talents and treasures to further the advancement of mankind. I thank the ISA society and my worldwide and global ISA family of over 33 years for giving me that opportunity.”

Zinschlag has resided with his wife of 49 years in Chesterfield, Mo., for the past 33 years. They have three daughters and seven grandchildren.