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Sunday, June 21, 2020

#437 Thirty years ago: June 1990

Papers published in June 1990 in IEEE Transactions on Electron Devices and IEEE Electron Device Letters exemplify significant interest at that time in gallium arsenide (GaAs), and in GaAs-based heterostructures in the variety of transistor configurations (MESFETs, HBTs, HEMTs). At that time GaAs was seen as a possible replacement for silicon in some cutting-edge transistor applications which, as we know now, did not happen. At least to an extent anticipated back then.


What caught my attention among other papers, were the reports on polysilicon and amorphous TFTs (Thin-Film Transistors) which shows growing interest in coming to life at that time active matrix displays technology where TFTs play key role.

Posted by Jerzy Ruzyllo at 03:53 PM | Semiconductors | Link

Sunday, June 14, 2020

#436 Remote college education

Because of the changes extorted by COVID-19, college education is forced to move, at least partially, toward remote learning, with no direct, personal-interactions with university professors and facilities (laboratories).  


While the remote learning may work for some majors, it will definitely not work for the engineering majors. Simply, there cannot be college-level education in the engineering without some kind of the hands-on experiences in the universities’ labs. Certainly not in the case of semiconductor materials/devices engineering. Obvious, but still worth stressing over and over again…

Posted by Jerzy Ruzyllo at 04:58 PM | Semiconductors | Link

Sunday, June 7, 2020

#435 Semiconductor market: inconsistent terminology.

 The reason why business community is using term “Semiconductor Market” in reference to what basically is a “Digital IC Market” is not clear to me. Semiconductor is a material displaying outstanding characteristics, differentiating it from conductors and insulators, which is used in applications far beyond digital (logic and memories) ICs. For some reason, other markets, also based entirely on semiconductor materials are referred to according to what they are. For instance, Analog IC Market, MEMS Market, Photovoltaic Market, LED Market, etc.      


 If this misguided terminology works for business/investments communities, that’s fine. The problem is that it also shows up in some semi-technical writings which should be more precise in using technical terms. For instance, only yesterday I came across an on-line report stating “…transistors, semiconductors, and other electronic components in the future….” Total confusion… What materials are transistors and most of those “other electronic components” made out of?


 By the way, if you are interested in this subject matter and would like to clarify some of the issues raised in this blog, you may want to take a look at my book “Guide to Semiconductor Engineering”. Just a suggestion…


Posted by Jerzy Ruzyllo at 11:58 AM | Semiconductors | Link

Sunday, May 31, 2020

#434 Thirty years ago: May 1990

After some twenty years of unobstructed progress through MOSFET’s (CMOS) channel/gate length scaling, in early 1990’s anticipated future challenges of digital IC technology were getting attention. The trend was exemplified by some papers published in May 1990 issue of IEEE Transactions on Electron Devices discussing undesired physical phenomena associated with channel length scaling in submicrometer CMOS devices, jointly referred to as “short-channel effects”. Specifically, Drain-Induced Barrier Lowering (DIBL), and hot-carrier degradation in the lower submicrometer devices were considered.


On the other hand, May 1990 issue of the Journal of the Electrochemical Society addressed a broad range of materials and processes related problems including metallization (tungsten silicide, nickel coatings, Au contacts to SiC), dielectrics (borosilicate intermetal dielectric, silicon nitride on GaAs and on InP), range of topics concerned with III-V compound device technology, for instance GaN films prepared by MOVPE, as well as with etching processes (for instance RIE induced deep levels, chemically assisted ion beam etching, or anisotropic photoetching of III-V compounds).

Posted by Jerzy Ruzyllo at 01:30 PM | Semiconductors | Link

Sunday, May 24, 2020

#433 What is a semiconductor, cont.

 Following on the previous blog… 


Another way of looking at the role of semiconductors and semiconductor devices is from the point of view of fundamental principle of energy conservation and ability of the material serving as a medium allowing exchange between various forms of energy. The machines, instruments, or devices we conceive, are constructed and used primarily for the purpose of energy exchange/manipulation  obeying the principle of energy conservation in the process.


Semiconductors, strictly speaking devices operation of which is based on the properties of semiconductor materials, allow versatility in exchange between various forms of energy unattainable with either metals or insulators


Properly configured devices based on semiconductor materials are unique in this regard allowing manipulation of electric energy associated with a flow of electric charge carriers (transistors for instance), exchange of electric energy into light (light emitting diodes), energy of light (energy electromagnetic radiation) into electric energy (image sensors, solar cells), thermal energy into electric energy (thermistors), and so on. And that’s what makes semiconductors so special.

Posted by Jerzy Ruzyllo at 09:18 PM | Semiconductors | Link

Sunday, May 17, 2020

#432 What is a semiconductor?

Broadly circulating definition of semiconductors stating that semiconductors are materials featuring electrical conductivity between insulators, for instance glass, and conductors, most commonly metals, does not adequately capture the essence of what is a semiconductor.


The essence is that under the normal conditions there is nothing that can be done to make copper more electrically conductive and glass less electrically conductive. In contrast, semiconductors are the solids which lend themselves to the manipulation of their electrical conductivity by orders of magnitude by altering their chemical composition. Also, in contrast to typical conductors and insulators, illumination with light featuring appropriate wavelength changes electrical conductivity of semiconductors. Furthermore, temperature may alter electrical conductivity of semiconductors to the extent not posible in the case of insulators and conductors (with an exception of extremely low temperatures at which some originally low-conductivity materials assume characteristics of superconductors).  


As a result, a vast array of extremely important in our lives devices (diodes, transistors, integrated circuits, LEDs, lasers, light and heat detectors, image sensors, broad range of other sensors, solar cells…..) function only because of the unique characteristics of semiconductors.

Posted by Jerzy Ruzyllo at 12:44 PM | Semiconductors | Link

Sunday, May 10, 2020

#431 Why organic contaminants are harmful in semiconductor technology?

Following on the earlier considerations of organic contaminants, let’s take a quick look at the ways they can interfere with semiconductor processing.


When allowed to agglomerate into particle-like colonies in the water delivery system, bacteria-based particles adsorbed on the exposed processed surfaces will have a harmful effect on the process just like any other particle in the semiconductor process environment.


Airborne volatile organics adsorbed on the processed surfaces in turn, if not removed prior to thin-film deposition on such surfaces, may lead to the major process malfunction. Prior to critical deposition steps such as for instance epitaxial deposition, organic contaminates will prevent high-quality film formation. Also, if not removed prior to the metal deposition, organic contaminants will results in the increased contact resistance.


Less obvious is a deleterious destabilizing effect of organic contaminants adsorbed on the wafers stored in between processing steps. What the terms “destabilizing effect” means, is that initially light organic compounds phsysisorbed of the surface are in the course of the prolonged exposure to the moisture containing ambient air chemically bonding to the surface changing its energy in the process. Such process is often referred to as “surface aging” and needs to be prevented, or strictly controlled in any semiconductor device manufacturing process.

Posted by Jerzy Ruzyllo at 07:40 PM | Semiconductors | Link

Sunday, May 3, 2020

#430 Viruses as organic "contaminants"

 Contaminants of concern in semiconductor processing include particles, metallic contaminants, and organic contaminants. The first are always of concern, the effect of metallic contaminants on the performance of the final device can be extremely damaging, or may be less harmful depending on the materials used, type of the process wafer's surface is subjected to, and temperature of the subsequent processe(s). Similarly to particles, organic contaminants need to be controlled at every stage of the device fabrication sequence as they destabilize semiconductor surfaces and may be responsible for the malfunction of the thin-film deposition processes, for instance.


The hydrocarbons airborne and outgassing from plastic containers used to handle, ship and store semiconductor wafers, as well as colonies of bacteria which may grow into a particle in some parts of the water delivery systems and then contaminate wafers, are of greatest concern with regard to organic contamination control in semiconductor manufacturing environment.


Isopropyl alcohol, IPA in short, and hydrogen peroxide (H2O2) are among most commonly used to remove bacteria and viruses from the surface of the objects we are touching in our daily lives, and from our skin. These are also solutions commonly used in semiconductor manufacturing to control organic contaminants. In addition, in order to prevent bacteria contamination, water used in semiconductor processing is strongly ozonated.


While the viruses as such may not directly affect/contaminate semiconductor surfaces, one thing is sure - there are no viruses either on the surface of semiconductor wafers processed in the course of semiconductor device fabrication, or in the water used in semiconductor processing. Wet benches used in semiconductor fabrication create a very viruses and bacteria unfriendly environment. As a result, no SARS-Cov-2 on the properly treated semiconductor surfaces and cleaning utensils during device manufacturing.

Posted by Jerzy Ruzyllo at 11:37 AM | Semiconductors | Link

Sunday, April 26, 2020

#429 Thirty years ago: April 1990

 As literature from exactly 30 years ago indicates, thirty years ago high-performance CMOS was getting into the territory of sub-quarter µm gate length (0.22 µm to be specific), and 3.5 nm gate oxide thickness. Literature further demonstrates (April issues of IEEE Transactions on Electron Devices and IEEE Electron Device Letters) strong focus on transistor technology in general. Weather it was field-effect MOSFET, MEST, MODFET, or bipolar HBT, the search for the innovative transistor solution for next generation digital circuitry was clearly on display.


Other than that, SOI technology, represented at that time by SIMOX substrates, was aggressively pursued. At the materials side, as papers in the April issue of the Journal of the Electrochemical Society indicate, the search for the gate dielectrics displaying higher k than SiO2 was gaining momentum. Except that it was focused on TiO2, Ta2O5, and zirconia (ZrO2) which later, as we now know, did not solve the problem high-k gate dielectric because of the insufficient thermal stability. 

Posted by Jerzy Ruzyllo at 03:18 PM | Semiconductors | Link

Sunday, April 19, 2020

#428 Semiconductor clean-rooms, virus protection, cleaning, cont.

Semiconductor clean-room apparel in general, including disposable and sterile clean-room garments, hoods, respirators, masks, gloves, shoes,  etc.,etc. are serving one purpose which is to protect pristinely clean environment from the particles generating people working in the clean-room. In other words, the goal is to protect the environment from us.


In the case of protection against viruses it is the other way around - the goal is to protect us against the contaminated environment. But the tools and means are exactly the same in these two cases.


Another example of semiconductor technology setting a tone for various virus-protection solutions is concerned with aggressively recently pursued use of UV light to clean surfaces and objects we touch in our daily lives. In semiconductor processing UV treatments of solid surfaces were explored (specifically for the purpose of organic contaminants removal) already over thirty years ago. See for instance this research paper: J. Ruzyllo, G, Duranko, and A, Hoff, "Pre-Oxidation UV Treatments of Silicon Wafers", Journal of the Electrochemical Society, vol. 134. p. 2052 (1987).


Posted by Jerzy Ruzyllo at 08:26 PM | Semiconductors | Link

‹‹ ›› is a personal blog of Jerzy Ruzyllo. He is Distinguished Professor Emeritus in the Department of Electrical Engineering at Penn State University. With over forty years' experience in academic research and teaching in semiconductor engineering he has a unique perspective on the developments in this technical domain and enjoys blogging about it.

This book gives a complete account of semiconductor engineering covering semiconductor properties, semiconductor materials, semiconductor devices and their uses, process technology, fabrication processes, and semiconductor materials and process characterization.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.


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