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material and device designs are selected in accord with the needs of either electronic or photonic functions. In the electronic case, the prime selection criteria include the width of the energy gap, the electron mobility, thermal conductivity, and certain manufacturability related properties. For photonic systems the key parameter is not only the width of the energy gap but also type of gap, either direct or indirect (Fig.1). Whereas historically, electronic and photonic functions were performed separately by designated devices made out of either electronic or photonic semiconductors, the present trend toward a merger of these two functions in a single material system is irreversible. Whether in present day and Photonics imaging system performance (in which the display quality is critically dependent by Andrew M. Hoff and Jerzy Ruzyllo on thin fi lm (TFTs) integrated with each pixel); or in solar cells (where Over the past fi ve decades a steady increase in both the quantity an electrical signal results from the conversion of radiated energy); or in and capability of electronic and photonic components that future generations of integrated circuits we may interact with on a daily basis has occurred. A stroll (where optical waveguides may one through an airport departure terminal at nearly any time of year day replace electrical interconnect lines effectively demonstrates this point. People may be observed while the underlying transistors carry out electronic operations), electrons and communicating with others by cell phone, working on are destined to interact closely , or checking the time on digital watches. Children within the same material system, or surround a portable DVD player to watch their favorite within the same device. -animated movie, while others play with miniature Electronic and Photonic hand-held video games as their parents listen to music from Materials and Devices pocket-sized MP3 players. Clearly the information age, that The basic materials and processes employed to fabricate individual or some believe began its steady rise with the demonstration of a discrete semiconductor electronic solid-state electronic component in a New Jersey laboratory in components have been known and in use December of 1947,1 has now become a global phenomenon. since the late 1950s. By that time had become the substrate material of Electronic computer systems that occupied large rooms and choice because of its adequate electronic used massive amounts of power were once accessible only to properties, availability, and, very large business concerns or to government entities. Present day importantly, the ease of formation of its high quality native oxide, SiO2. Methods computer systems with greater functionality run for hours on of surface preparation such as cleaning the sets of rechargeable batteries and fi t nicely on a person’s lap. silicon surface to remove yield-limiting Electronic and photonic components constitute and support a trace impurities,2 doping, and pattern defi nition, were in development along major portion of the global economy and strongly contribute with high temperature chemical process to the effectiveness of business, education, healthcare, and techniques that formed a passivating entertainment sectors. and durable layer of SiO2 glass on the surface of the single-crystal silicon.3 The importance of silicon in electronics was The ECS Electronics and Photonics systems forms a basis for the development further enhanced when, in the late 1950s Division fi nds itself in the center of the and manufacture of electronic and two working independently action on the semiconductor electronics photonic devices and systems. The in Northern California and in Texas, and photonics arena since the invention difference between these two is that in the respectively, developed schemes to of the followed by the invention former electrons act as the information integrate multiple electronic components of the emitting diode. In this brief carriers, while in the latter the same within a single semiconductor body. overview, the technical and scientifi c function is performed by photons. An This innovation, the foundations upon which the presence electron is a negatively charged particle or IC, formed the foundation for an of this Division is established as well in an atom and carries the smallest, or unprecedented growth of semiconductor 4 as the Division’s mission and goals are elemental, electric charge. A is electronics. presented. basically a packet of electromagnetic The following decades have produced energy that can be tailored to perform a continuous stream of innovations Electrons and Photons various functions in information aimed at addressing the challenge of A fundamental ability to control the processing systems. properties of materials and material (continued on next page)

36 The Electrochemical Society Interface • Spring 2006 Electronics... have yielded both lattice-matched as (continued from previous page) well as lattice-mismatched or strain-layer superlattices and complex heterostructures with highly engineered bandgaps. This capability has enabled advanced photonic devices such as LEDs and , as well as electronic structures, e.g., heterostructure bipolar transistor (HBT) development. In addition to light emission technologies, this new generation of III-V and II- VI compounds now provides for the effective detection of light over a broad spectrum of culminating in the detection of UV radiation due to the mastering of wide-bandgap compounds such as GaN and ZnS (Fig. 1). Over the course of electronic and photonic device manufacture, the respective materials, e.g., Si in the former case and GaAs in the latter, had been considered entirely incompatible with each other both from the chemical FIG. 1. Selected semiconductors and properties determining their usefulness in electronic and photonic composition viewpoint (Ga and As applications. are dopants in silicon while Si is an providing ever-increasing capability or and mechanical properties of silicon are amphoteric dopant in GaAs) and from a functionality in a given area of substrate merged to carry out unique functions. crystallographic structure viewpoint. This paradigm is slowly changing not only material. Over this period the dominant Single crystal silicon is certainly a due to the earlier mentioned emphasis semiconducting substrate material has work horse of semiconductor electronics. on the merger of electronic and photonic remained silicon for the majority of ICs In addition to its dominant role in IC functions that will blur the boundaries manufactured; although compound technology, silicon is also used in a broad between these two domains; but also semiconductor materials, primarily range of discrete device applications. due to the likely merger of high-electron GaAs, continued to increase in usage in Silicon appears as thin films of amorphous mobility compounds such as GaAs various electronic applications such as or polycrystalline form in TFT technology, and InSb (Fig. 1) with silicon in next wireless communication, microwave, in solar cells, and in other applications. generation CMOS IC technology, where and high-speed digital systems. For As the range of electronic applications for an increased mobility of electrons the all semiconducting substrates the continues to expand, however, the channel can conceivably be made out of planar technology of need to supplement silicon with other III-V compound semiconductor. devices dominated over this period. semiconductors is evident. For instance, The fabrication scheme employed for SiGe is needed to introduce electron- Until recently all functional a typical circuit involves a detailed accelerating strain in the Si lattice, semiconductor materials originated from sequence of additive and subtractive layer whereas itself, with its the semiconductor series of the periodic formation and patterning steps. State- superior electron mobility over Si, may table. They are available as bulk wafers of-the-art complementary metal-oxide- see a resurgence on the semiconductor or as thin films deposited primarily on semiconductor, or CMOS, circuits employ arena. In addition to Ge the wide-bandgap mechanically stable and limited-size twenty or more layers and masking steps silicon compound, silicon carbide substrates. A new breed of semiconductor to obtain the final device. Innovations (SiC) (Fig.1), has steadily emerged as a materials, known as organic in both the materials employed (such prime candidate for high-power, high- semiconductors, consisting primarily as the increasingly broad use of SiGe in temperature device applications despite of carbon, hydrogen, and oxygen, is both bipolar and unipolar silicon devices), continued problems with substrate quality bound to overcome these limitations and in the fabrication approaches to and a high density of interface traps at the and expand semiconductor electronics forming ever smaller structures in the and photonics into new areas. Regarding SiO2-SiC interface in MOS devices. layers, have enabled manufacturers to this expectation, organic semiconductors A few years after the breakthrough provide increasingly complex and capable may be deposited inexpensively on invention of the IC, a development digital and analog devices. Progress large substrates, most thin-film organic important to photonic applications took in manufacturing tools including, in semiconductors maintain their properties place when a physicist in upstate New particular lithographic tools, is allowing even if their substrates are drastically York demonstrated the first solid-state still higher resolution of the pattern flexed or deformed, and they are capable visible light emitting diode (LED) using transfer process. Current geometries of of emitting light in the visible region. compound semiconducting material.5 cutting edge ICs are in the 65 nm range The emergence of such large-area plastic Since then an avalanche of progress and are bound to get even smaller. In electronic and photonic structures allows involving III-V compounds including this sense, semiconductor technology us to anticipate an exciting future of these GaAs, InP, and GaP, has occurred entered the realm of technical domains. several years ago and continues to serve culminating in the development of a blue 6 as a technology driver for emerging semiconductor using GaN (Fig. 1). Progress in Semiconductor scientific and technical domains such An advancing understanding of the Electronics and Photonics Continues and chemistry of III-V compounds as spintronics and bioelectronics. In Progress in electronics and photonics is and progress in vacuum technology, that addition, silicon is broadly used to as much dependent on continued trends allowed for the development of very- fabricate microelectromechanical systems as it is on single developments such high-precision deposition techniques (MEMS) in which the favorable electronic as the emergence of specific technical such as molecular beam epitaxy (MBE),

The Electrochemical Society Interface • Spring 2006 37 solutions. The list of both is long. Here are a few examples of the trends and specific technical breakthroughs needed to sustain the desired progress in semiconductor electronics and photonics. Early circuit structures employed layers with vertical and horizontal dimensions relative to the plane of the substrate surface on the order of micrometers whereas present-day circuit dimensions have been scaled down to the nanometer region. Among the various FIG. 2. MOSFET evolves over the years to meet growing performance requirements. Structure of the improvements mentioned earlier, MBE contemporary high end MOSFET (b) differs significantly from an original (a). Future generation MOSFETs, was instrumental in assuring control over such as (c) FinFET shown must be modified further.8 vertical dimensions while control of the horizontal dimension in conventional as the charge needed to represent a digital applications. technology still depends on the resolution zero or one in memory devices approaches This section has mentioned a few of lithographic processes. The use of the limit of a single electron, quantum technical developments that either have resolution enhancement techniques structures are being applied to provide or will play a critical role in allowing for such as phase shift masks, immersion multiple electronic states in the same area, the sustained growth of the electronics lithography, as well as a new generation e.g., a two state structure provides twice and photonic industries. However, of photoresist and excimer lasers, allows the memory density in the same area. additional advancements are needed. In photolithography to remain effective Over the past fifteen years, the this regard, ECS assists in the creative down to the 45 nm resolution level. shrinking or scaling of dimensions in process by maintaining an intellectual Furthermore, innovative approaches to electronic and photonic structures has environment that supports such progress the fabrication process, the selection of challenged manufactures to search for and innovation. the materials employed, and new MOSFET alternative dimensional measurement designs (Fig. 2) were developed to achieve approaches. Higher precision relative to Electronics and Photonics at ECS dimensional scaling and improved circuit the dimensions being acquired is needed performance. Chemical mechanical Technical societies have been formed to quantify and monitor the progress and planarization (CMP), which had been to facilitate effective interchange of outcomes of the fabrication processes at used extensively in the production of information and ideas between members numerous stages in the layer sequence. the initial high quality silicon substrate of the global scientific and technical For example, glass films intended to wafers, was applied to the planarization community. ECS and its constituent be 1 nm thick must be measured with of the dielectric and metallic films used Divisions, including the Electronics a precision of 1% or less. In addition to interconnect the millions of transistors and Photonics Division, provide such to dimensional metrology, measured in the substrate body. CMP processing an important service to the global parameters regarding the quality or provided many benefits such as an community by broadly disseminating cleanliness of both the surface and bulk increase in the maximum number of information. Timely publication of regions of device structures and substrates interconnecting layers on a circuit, an information is accomplished both in is now being driven well below the part improvement in the reliability of the print and in electronic media and in per billion level using X-ray, electron overall interconnect structures, and an particular at meetings of the Society held beam, and photon sampling of the improvement in the manufacturing yield twice a year where topical symposia are surface/bulk regions of the materials. At and productivity.7 an important venue for dissemination of present the silicon substrate diameter used new knowledge and methods of interest The need for control of the quantum in manufacturing is in transition from 200 to meeting attendees. The Electronics transport of charge carriers in electronic to 300 mm and is expected to move to a and Photonics Division sponsors or co- materials has led to both reliability issues diameter of 450 mm within the next ten sponsors over 40 such symposia. These and to opportunities regarding the gain years. The expense of the larger substrates symposia cover a broad range of topics of MOS transistors. As the dielectric is causing manufacturers to search for related to state-of-the-art semiconductor thickness of the gate oxide layer between in-line metrology solutions that may be electronics and photonics. A majority the control gate and the conducting applied to product materials rather than of these symposia are internationally channel of the field effect transistor to process witness substrates that were established and are traditionally attended has decreased, quantum mechanical once commonly used in manufacturing. by top scientists and researchers from tunneling or leakage of carriers between In addition, new metrology approaches around the world. Part of the success the gate electrode and channel has are being sought that will provide of these endeavors is that the list of occurred. New higher dielectric constant quantitative electrical properties of device symposia is continuously updated to insulator materials which allow a thicker layers and structures prior to completion reflect emerging needs and trends in film to be used and still induce an of the overall device structure. electronic and photonic materials, process equivalent charge in the channel to that Exciting developments resulting technologies, and device structures. formed by a thinner glass insulator, are from a broader application of bottom- being evaluated as a replacement for the With a membership of around 2,000, up processes should add new flavor to SiO glass films that have been in use for the Electronics and Photonics Division at 2 the next-generation implementation of forty years. This transition will likely be ECS has a critical mass sufficient to play electronic and photonic device functions. accompanied with a switch from poly-Si a lead role in the international solid- In this regard the accomplishments of gate contacts in next generation CMOS to state science and technology arena. More surface science and solid-state chemistry metal gate contacts. As mentioned earlier, important than the number of members, could be effectively translated into the to further address the transport control however, is that scientists, researchers, technology of self-assembled monolayers, of carriers in the channel of MOS devices, and engineers from around the world or SAMs, which are bound to play key strain is being applied as a tool to improve roles in future electronic and photonic (continued on next page) the conductivity of the channel. Finally,

38 The Electrochemical Society Interface • Spring 2006 Electronics... References (continued from previous page) 1. M. Riordan and L. Hoddeson, Crystal Fire, May 7-12, 2006 associated with this division, represent the W.W. Norton & Company, New York (1997). highest level of professional competency. 2. W. Kern and D. A. Puotinen, RCA Rev., 187 Denver, Colorado Incidentally, one important function of (June 1970). the Electronics and Photonics Division at 3. B. E. Deal and A. S. Grove, J. Appl. Phys., 36, 3770 (1965). ECS is to identify and to recognize leaders October 29- 4. R. N. Noyce U.S. Pat. 2,981,877 (1961); J. S. in the fi eld by awarding one of them every Kilby, U.S. Pat. 3,138,743(1964). November 2, 2006 year with a prestigious Divisional award. 5. N. Holonyak, Jr. and S. F. Bevacqua, Appl. It is in this environment in which less Phys. Lett., 1, 82 (1962). Cancun, Mexico experienced members of the community, 6. Compound Semicond., 2, 7 (1996). graduate students in particular, should 7. J. G. Ryan, R. M. Geffken, N. R. Poulin, and fi nd great opportunities to learn and to J. R. Paraszczak, IBM J. Res. Dev., 39, 371 May 6-11, 2007 (1995). expand their professional horizons. 8. J. Ruzyllo, http://www.semi1source.com/ Chicago, Illinois Summary notes/ Electronic and photonic devices and About the Authors October 7-12, 2007 systems have developed into a dominant ANDREW M. HOFF is an associate professor of Washington, DC global industry over the past fi fty years. As electrical at the University of South we move forward in the new millennium, Florida in Tampa, Florida. His research focuses the structures and materials used to on novel semiconductor oxidation processes and manufacture devices and systems will on in-line semiconductor materials and thin-fi lm characterization methods. He is a Member-at-Large likely change signifi cantly from those that of the ECS Electronics and Photonics Division and have supported this revolution until now. may be reached at [email protected]. Through its publications, symposia, and JERZY RUZYLLO is a professor of electrical other means of knowledge dissemination engineering and and engineering the Electronics and Photonics Division of at The Pennsylvania State University. His research ECS intends to continue contributing to is in semiconductor manufacturing science and For more information on these the development of future information engineering with emphasis on semiconductor surface future meetings, contact the processing and characterization. Professor Ruzyllo Society Headquarters office. and communications systems. We are is Chair of the Electronics and Photonics Division counting on the next generations of of the Society. He is a Fellow of ECS and a Fellow of Tel: 609.737.1902 scientists, researchers, and engineers to IEEE. He may be reached at [email protected]. FutureFax: Technical 609.737.2743 Meetings continue this mission for many years to www.electrochem.org come. 

The Electrochemical Society Interface • Spring 2006 39