The Birth of Glow Discharge Chemistry and involvement of the Author in a Lifetime pursuit of Semiconductors

by R C G SWANN CEng MIET MIEEE

This paper documents some of the research performed by the author at Standard Telecommunication Laboratories, Harlow, Essex (1959 -1966) and subsequently at the Shockley Laboratories in Palo Alto, California (1966 – 1968) and at ITT Semiconductors in West Palm Beach, Florida (1968 – 1971). The main body of the paper is focussed on the development and continuing success of the glow discharge process particularly over the last 50 years. This paper also extends into the author’s role of Corporate Auditing of Semiconductor Suppliers and their technologies, during the second half of a career in semiconductors, implemented at ITT and subsequently at their successor, Alcatel, also in Telecommunications.

Introduction to Standard Telecommunication Laboratories:

Standard Telecommunication Laboratories (STL),located on a 17acre site, London Road, Harlow, Essex, England was a purpose built facility completed in August 1959 by Standard Telephone and Cables (STC) which, in turn, was owned by the industrial conglomerate International Telephone and Telegraph Corp. (ITT) of New York. Richard (Dick) Swann was amongst the first transferees to STL in September 1959 and awaited completion of the designated lab.
The organisation comprised around 500 staff, extending to 1000 staff at its peak, mainly of scientists and engineers with personnel coming from STC Labs located in Enfield, Middlesex. and from Ilminster, Somerset; the latter under the leadership of Henry Wolfson. Swann came from the latter organisation in 1959, where he was previously engaged in the development of thermistors and then transistors. This early work on transistors will be lost in the mists of time as will be the small laboratory on the site of the old Dowlish Ford Mills rope factory at Ilminster which pioneered and manufactured thermionic valves on this site in the 1940s, followed by development of Thermistors and Transistors (Point Contact and Junction Alloy Transistors) in early 1950s where Swann worked, under Tony Settrington (Thermistors) and Stan Sheppard and Geoff. Walker (Transistors), in the role of laboratory assistant.

STL is acknowledged as the birthplace of a number of significant inventions including optical fibre communications by Charlie Kao and George Hockham and recognised by a Nobel prize awarded to the former. Prior to that work, Pulse Code Modulation had been invented by Alec Reeves whilst working at the ITT Labs in Paris before continuing his work on optical communications at STL. Significant work was also performed on III/V Semiconductor Compounds and associated devices under Chris Dobson and Peter Selway. Novel switching devices using glassy layers sandwiched by two metal electrodes and high voltage junction bevelled transistors as well as the technique of fibre pulling for low loss optical fibres were developed under Cyril Drake and variously assisted by Ken Ellington,Tom Cauge, Ian Scanlon and others. Also, high atmospheric pressure research was carried out using anvils and hydraulic presses to create synthetic diamonds under Prof. Colin H. L. Goodman and Dr. John Lees.

STL, acquired in 1991 by Northern Telecom (headquartered in Canada and later known as Nortel) was integrated into their Bell Northern Labs. In mid 2000 Nortel filed for Chapter 11, signalling the ultimate demise of STL and the end of around 50 years of significant scientific inventions. A more complete history of STL , may be found in the article ‘A Brief History of STL’ by Vi Maile.

The Birth of Glow Discharge Chemistry for Inorganic Thin Films:

This chapter is focused on the birth of glow discharge chemistry, at STL leading to the deposition of a range of materials hitherto thought impossible to create at such low temperature. This fundamental finding and technique of enabling chemistry at temperatures well below those used in pyrolytic decomposition reactions, is still paving the way into the new nanotechnologies such as carbon nanotubes and graphene material as well its use for fabricating micro-cavity OLEDs (Organic Light Emitting Diodes) and Solid State Lithium Ion Batteries. Studies in the bio-medical field are emerging where surface treatments of materials may be advantageous for implanted devices with research in Japan on substrates for cell growth.. The plasma chemistry concept has already resulted in a multi-billion dollar business for the production of semiconductor integrated circuits (ICs), Thin Film Transistors (TFTs) for flat panel displays, LEDs and solar cells apart from the manufacture and sales of plasma deposition equipment and the provision of a range of material depositions on customers substrates by service labs.
The fundamental principle continues to spawn new studies and is the subject of many research programmes at Institutions and Universities around the World, demonstrating that glow discharge chemistry still evokes the imagination and curiosity of the researcher nearly 50 years later.

The derivation of the basic invention was an outcome of early work in a study of the growth of epitaxial silicon layers on single crystal polished slices of silicon. That process was established using a vertical quartz reaction tube inside which was positioned a carbon or molybdenum susceptor to which radio frequency (rf) energy could be inductively coupled, for localised heating purposes, from an external coil and rf generator.The susceptor also formed the horizontal pedestal for holding the silicon wafer. The quartz reaction tube was fed with a precursor and carrier gas.
A research team was set-up by Dr. Joe Evans (Materials Division Manager) who appointed H. (Henley) F. Sterling whose past experience was in growing single crystal ingots from seed crystals of germanium and then silicon by the Czochralski method using a water cooled crucible and r.f heating. Also. the associated development of float zone polysilicon ingot purification in a water cooled silver boat using r.f. energy and its resultant levitation, for sweeping impurities, held in the molten zone, from one end of the ingot to the other.

A plan was established for the newly assembled team to investigate, firstly. the feasibility and then the optimum conditions for silicon epitaxial growth using three different source chemicals preceded by the design and construction of their respective apparatus. Each process to be managed by an assigned process engineer, namely: Silane (SiH4) under Swann, Silicon Tetrachloride (SiCl4) under Mike Taylor and silicon iodide (SiI4) under H. Sterling. The latter process was terminated within 1 year, since process control was difficult. The remaining two processes were further developed and optimised in respect of crystal perfection and growth rates. The author is indebted to D (Dave) J. D. Thomas for sharing his expertise and giving guidance on matters of crystallography as well as the early use of the Scanning Electron Microscope (SEM). The silicon tetrachloride process yielded higher growth rates but the process suffered from auto doping of impurities.
It was decided to continue investigations with both processes to ready them for production and to concentrate on enhancing the growth rate of silicon from silane. The approach was to increase the streaming velocity and explore the impact of low pressures by partial vacuum within the reaction tube.

This led to the significant finding of the feasibility of glow discharge chemistry for the deposition of amorphous silicon, which became known as plasma enhanced chemical vapour deposition (PECVD). We demonstrated that thin films can be deposited at room temperature without thermal activation,

At STL, we studied the feasibility of performing the chemistry of depositing glassy vitreous/ amorphous silicon films from silane (SiH4), silicon carbide from silane and methane (CH4) or methyl silane (CH6Si), germanium from germane (GeH4), carbon from methane (CH4) but concentrated on silicon dioxide from silane and nitrous oxide (N2O) and especially silicon nitride (Si3N4) from silane and ammonia (NH3) for its potential to support not only ITT’s own semiconductor industry but subsequently the Worldwide industry. The latter application was a ‘first’ in terms of demonstrating capability and obtaining more reliable semiconductor devices when depositing passivation layers of silicon nitride, silicon oxynitride or silicon dioxide, singly or in combination, at a temperature well below that of a thermally activated chemical process for silicon nitride. Publication of these findings was withheld for some considerable time until patent descriptions were written and an Application submitted to the Patent Office in 1964.

Presenting the Glow Discharge Process to The World:

Initially, French, British and US Patents were applied-for (1964 and 1965) in respect of the basic invention in the names of Henley Frank Sterling and Richard Charles George Swann. Following the Patent Applications, Swann was directed by STL Management to present the glow discharge findings at various conferences and to publish in scientific journals. It was, however, at The Physics Society Exhibition in Manchester (April 1965) where the glow-discharge equipment, designed and built at STL, was demonstrated by Swann and Dave Thomas, which resulted in a Worldwide interest. Many enquiries and requests for feasibility and sample preparations were made including: part of a jet engine turbine blade, nylon material from the fabric/garment industry, paper from the newsprint industry, leather from the shoe industry, strip steel from a steel mill, and anti reflective coatings on optical glass etc.

Transfer to the Shockley Labs, Palo Alto, California:

In early 1966, Swann was invited to the ITT Shockley Laboratories, Palo Alto, California, to continue the glow discharge studies and contribute to the emergence of the integrated circuit technology (in the yet to be named “Silicon Valley”). The Shockley Labs were originally established by William Shockley, co-inventor of the transistor, and were subsequently owned by the Clevite Corp. and then acquired by ITT in 1965.
The first step by Swann, at the Shockley Labs, was to build the plasma equipment and study the properties of the resultant insulating layers in the context of the emerging metal gate PMOS/CMOS device technology. The most significant findings were in respect of demonstrating the excellent barrier to sodium when employing silicon nitride as opposed to the standard silicon dioxide dielectric; as well as the excellent compatibility of the plasma deposition process with existing semiconductor technologies. The electrical charge impact on the MOS gate was also studied in detail. Further experimental work was carried out to demonstrate the feasibility of doping silicon using elemental species by using plasma deposited layers for which a patent was filed by Swann and Cauge in March 1968.

Transfer to ITT Semiconductors, West Palm Beach, Florida:

In 1968, Swann was asked by ITT HQ in New York to set up a new state-of-the-art cleanroom within their existing bipolar transistor/integrated circuit operation in West Palm Beach, Florida. The plasma process was scaled-up in a 10 inch bell jar to handle multiple wafers and in addition early pioneering work was performed on a poly crystalline silicon gate technology which of course became the industry standard. Patents were filed in January 1971 by Swann and Penton and in September 1973 by Harlow, Swann, Penton and Bakker in the context of silicon gate NMOS technology. A study of the properties of Silicon Dioxide, in a glow discharge, from the precursor gases of SiH4 and CO2 were published by Swann and A E Pyne , in 1969. A Silicon gate MOS Integrated circuit was also demonstrated by converting a licensed Fairchild Multiplexer from Metal (Aluminium) Gate to Silicon Gate MOS with much improved performance and subsequently its conversion from PMOS to NMOS technology.

At the conclusion of Swann’s career in semiconductor research, a total of 13 patents were issued in co-authorship with different collaborators at various ITT laboratories. The subject areas were in the realm of either thin film glow discharge chemistry or in novel semiconductor device structures. The Patents issued, embraced 5 countries, namely: the UK, USA, Canada, Germany and France.

Return to STL Harlow:

In 1971, Swann was reassigned to STL Harlow as Chief Scientist, reporting to ITTs Worldwide Semiconductor Corporate Technical Director (Dr Herb, Renner) in New York. The objectives were to oversee the setting-up of a silicon gate process to yield a 4×4 Crosspoint electronic switch for ITTs state-of-the-art switching system, as well as overseeing research programmes in ITT’s research and manufacturing locations in Footscray – England, Freiburg – Germany, West Palm Beach – Florida and at Shelton – Connecticut.

A Career Change in Semiconductors:

In 1974, ITT Europe HQ in Belgium, requested assistance to establish a system for the assessment and control of their semiconductor component suppliers of which there were many new emerging suppliers and new technologies. The Supplier Assessment Program embraced the setting up of Standards and a System for on-site assessment visits to Semiconductor Suppliers to evaluate their capability from an Organisational, Quality and Manufacturing point of view but even more importantly to record a confidential detailed, step by step, process flow chart with baseline parameters to assess integrity, reliability, manufacturability and the ability to monitor change especially in the context of the fast growing ‘custom integrated circuit field’. Reporting was made to Corporate Purchasing with Supplier Reports going to all Component Managers in all the Worldwide Telecom operations of ITT. Swann joined an existing group of Component Managers at The ITT Europe Engineering Centre in Harlow, in the role of Manager of Semiconductors- Integrated Circuits.

The system, established by Swann, was well acknowledged within the Worldwide Corporate Purchasing Department and by all manufacturing operations of ITT as being a sound, cost saving measure (minimising product failures, supply issues and a harmonised procurement system across ITT) and in turn by Suppliers who saw the benefits of the most rigorous third party Audits they had experienced with detailed and constructive critiques. The system was adopted by Alcatel, France upon their purchase of ITT’s Telecom. Operations in 1986. This work provided Swann, who was based at the Alcatel HQ in Paris and then at Alcatel ITS in Zug. Switzerland, with a unique insight into the Worldwide Semiconductor Industry and its technology which in his career spanning 45 years witnessed the evolution from 1 inch to 12 inch diameter silicon wafers (now going to 18 inches) and feature sizes reduced from 10 microns to <0.25 microns with Photolithography moving from In-Contact Printing to Steppers and Laser I-line Projection equipment, wet etching transitioning to dry plasma etching, MOS gates moving from aluminium to poly silicon, the universal application of PECVD and planarisation progressing from isoplanar structures and reflow glasses to CMP (Chemical Mechanical Polishing).

The statistics, of the supplier and technology assessment activity over 25 years, upon reflection, are quite amazing e.g.

• . Assessment of > 60 Semiconductor Companies
• . Visited and assessed > 115 Wafer Fabrication manufacturing locations
• . Assessed a Total number of Wafer Fab. Lines > 250
• . Similar statistics were accrued for Assembly and Test Operations Worldwide.
• . Travelled on 3000 flights and 130 Airlines and visited 47 different Countries

A few of the extreme Audit findings identified, and not previously declared, included;

• • In one case the lack of a Quality Department, in another, the lack of a Quality Manager, another case where the Quality function was directly involved in production and in many cases the lack of meaningful documentation and statistical process control.

• • A Wafer Fab line had been shutdown for more than 2 weeks whilst a source of contamination had still not been identified during the Audit.

• • A factory in China, where excellent documentation prevailed, was ‘set-up’ by the Company, for the ITT assessment inspection, with workers performing tasks but, in fact, it was found that the factory had not been in production for more than one year!
    Plastic moulding compound was stored in a cafeteria refrigerator together with food!

• • Due to manufacturing difficulties a contracted Company had subcontracted part of the process and in another case the entire process, both in violation of the Contract terms.

• • The layout of a factory floor was better known by the Inspection team than by the Manager hosting the Audit .

• • Some bizarre events, disturbing the ongoing/planned inspection, included: a leaking poisonous gas, a fire in the wafer fab, the death of a worker falling through the roof of the factory and a severe destructive earthquake.
  • The Semiconductor Corporate HQ of a large European Company did not know of the existence of its wafer fab and assembly line in the South Pacific, belonging to another Product Division of the Company

In summary, a unique career in the silicon semiconductor industry from its inception to its growth in Silicon Valley and beyond. The opportunity to be involved in the grass roots development and patenting of glow discharge chemistry and especially to demonstrate the advantages of silicon nitride in respect of the improved reliability of integrated circuits. To be also at the forefront of development of the silicon gate MOS technology which is still the workhorse of today’s technology. Also, perhaps the greatest reward, in that plasma chemistry is still, today, the subject of continuing interest in the development of new technologies and devices, particularly in more than 30 Universities Worldwide,

Swann was awarded the coveted ‘ITT Ring of Quality’ award in June 1983 at a ceremony in Lisbon, Portugal for his contribution to Semiconductor Technology and the Quality Control of purchased semiconductor products.

APPENDIX – A – Patents Granted:

This is an abridged version of the original documents which was written for the history section of IEEE (the American Institute of Electrical and Electronic Engineers) website. The full version including a comprehensive list of citations may be found at the following link.