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Sunday, July 19, 2020

#440 Silicon vs silicone

As a semiconductor purist, I can’t help, but take note of  all too often encountered misuses of semiconductor related terms (see for instance entry #435). As an example, a quote from the piece I recently came across on-line: “…. the plastic mask is secured to your face with a silicon pad…”

 

I won’t get to into explaining the difference between “silicon” and “silicone”, because it is so obvious. I am just protesting against frivolous misuse of the name of my favorite semiconductor.  Little “e” makes a big difference...

Posted by Jerzy Ruzyllo at 11:17 AM | Semiconductors | Link


Sunday, July 12, 2020

#439 Surface aging

Surfaces of semiconductor wafers during handling, storage, shipping, etc., are unavoidably exposed to moisture, oxygen, and volatile organic compounds present in the surrounding ambient air regardless of whether it is an ultra-clean clean-room, plastic shipping container, or storage box.

  

The process of adsorption on the wafer surface of the air-born species listed above gradually changes chemical composition of such surface and accounts for what’s known as surface” aging”. As a result, in the matter of days regardless of whether initially hydrophobic or hydrophilic, surface is losing its original wetting characteristics reflecting changes in the surface energy. At its early stage the process of surface “aging” can be reversed by means of the discussed in the previous blog lamp cleaning. If allowed to continue for the longer period of time (e.g. prolonged storage of wafers between processes), only conventional wet cleaning is able to return the surface to its original condition.

Posted by Jerzy Ruzyllo at 05:13 PM | Semiconductors | Link


Sunday, June 28, 2020

#438 Lamp cleaning

Earlier blog #428 was concerned with UV (185 nm and 254 nm) cleaning used in semiconductor processing for the purpose of organic contaminants removal from the processed surfaces. As we all know now, UV light (especially far-UVC, 222 nm) is used for disinfection which basically comes down to the annihilation of organic “contaminants” (if the use of the term “contaminants” in reference to viruses and bacteria is appropriate).

 

The problem with UV is that it needs to be used (wavelengths selection) very carefully because either through ozone generation or direct exposure it can be very harmful to us.  On the other hand, oxygen plasma, which is even more effective than UV in organic contaminants removal, cannot be easily implement not in the reduced pressure environment.

 

An easy to carry out alternative to UV irradiation is the use of much longer wavelength infrared lamps and use heat generated by such lamps (halogen for instance) to remove organics from the solid surfaces in ambient air. It is well known that heat kills viruses and bacteria. Just like in the case of UV cleaning, such IR lamp cleaning was shown very effective in semiconductor processing (e.g. A. Danel, C. L. Tsai, K. Shanmugasundaram, F. Tardif, E. Kamieniecki, J. Ruzyllo, “Cleaning of Si Surfaces by Lamp Illumination”,  UCPSS 2002, Solid State Phenomena, vol. 92, 196-198 (2002)). When properly implemented (temperature, time of exposure) it is also effective in neutralizing viruses and bacteria.

 

Yet another example how the high demands and experiences of semiconductor processing can be employed in our daily lives

Posted by Jerzy Ruzyllo at 07:55 PM | Semiconductors | Link


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


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Semi1source.com/blog 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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