The 221st ECS meeting (Spring meeting of the Electrochemical Society) just got started (May 6-10). You can easily check what's going on in terms of meeting's program. You may be particularly interested in symposia E1-E7 dealing with a broad range of semiconductor related topics.

As it is a blog #200 it is a bit of the milestone. I started 4.5 years ago, in December of 2007 to be exact, and since then it has become a habit of mine to share a little something about semiconductors about once a week. As it is a side “project” for me I find time to share my observations mostly over the weekends. Not having much of the response in terms of comments posted on this site I don’t quite know whom I am reaching and with what results. But, what can I say, a hobby is a hobby and I will keep on blogging about semiconductors for as long as I will have fun do it it. Cheers!

The III-V semiconductor compounds, synthesized using elements from groups III and V of the periodic table continue at the accelerated path their expansion into commercial device territory. Considering a number of combinations in which group III and group V elements can be put together to form a functional semiconductor, sorting through the pool of resulting III-V materials in an attempt to figure out what is what in terms of physical properties is not an obvious task. The fact that  in most cases these compound semiconductors are used in device fabrication in the form of ternary (III-III-V) rather than binary (III-V) compounds adds to the confusion with regard to criteria that can be used to sort them into the classes of materials based on distinct electronic properties.

Sensors are the devices that can detect changes in the physical or chemical environment and convert them into measurable signal such as electric current. I am not sure we fully appreciate the level of saturation of our daily lives with sensors and the critical role  they play in determining how we function.

Whether it is to satisfy the needs of next generations ultra-low power logic ICs, or cost-effective photovoltaics, or lighting LEDs, or infrared photodetectors the pool of elements semiconductor industry is drawing from expands continuously.

Among only three elements (carbon, C, silicon, Si, and germanium, Ge) displaying device-useful semiconductor properties, silicon is, and will continue to be in the foreseeable future, the most important. It doesn’t look like applications of germanium will grow spectacularly beyond its current use. Situation with carbon, however, is quite different.

Previous comments on electrical characterization brought to mind the problem of process monitoring. The increased cost of wafers and costly fabrication processes involved in the manufacture of sub-50 nm ICs call for rigidly executed, reliable monitoring of the nanochips fabrication process at its various stages. To be effective, process monitoring must be carried out in-line in real time on production wafers which requires totally noninvasive quickly executed measurement which provides unambiguous information about condition on the condition of the surface of the processed wafer.

Continuing on the challenges electrical metrology of semiconductors and semiconductor material systems is facing these days...

There are several factors that affect electrical characterization of extremely confined both vertically and horizontally semiconductor material systems we commonly deal with currently. Let me refer to just three of them to make a point.

First, most of the common electrical characterization techniques do not work well with semiconductor films as thin as those used today in advanced devices. For instance, even as routine task as determination of resistivity requires special measures to be taken in the case of ultra-thin epitaxial layers.

Second, to assure reliable determination of any given electrical parameter of semiconductor,  low resistance ohmic contacts to the measured material need to be formed. Considering wide range of semiconductor materials currently used to fabricate devices it is not a trivial task as for each composition (e.g. ternary semiconductor compunds), a metal forming very low resistance contact must be used.
 

Third factor to be considered is related to the fact that semiconductor structures that need to be electrically characterized are often not planar. A good example would be a nm-sized vertical, "fin"-shaped geometrical features to be used as channels in next generation MOSFETs, known as FinFETs. Determination of basic electrical characteristics (resistivity, electron mobility or carrier lifetime) of such structures without making a transistor is a true challenge.

Among methods used to determine selected key characteristics of semiconductors and semiconductor material systems electrical measurements provide the most direct, quantitave information. This is becasue electrical measurements determine characteristics of semiconductor material that we know will determine performance of the device fabricated using material. For instance, if through the capacitance-voltage measurements it is determined that any given semiconductor-dielectric structure features very high density of inteface traps then we can be certain that this particular combination of materials can not be used to fabricate high-performance MOSFET (Metal-Oxide-semiconductor Field Effect Transistor). Or, if through electrical characterization we learn that the select operation preformed on the wafer in the course of device manufacturing adversely affects, for instance, electron mobility of semiconductor  then we know that the process needs to be modified before it could be used effectively.

Overall, electrical characterization of semiconductors is very well established and plays pivotal role in semiconductor R&D. Recently, however, many among established method and methodologies of electrical characterization are being challenged by drastic changes in the geometry of comples semiconductor material systems used to fabricate functional devices. In short, some key electrical characterization techniques that are very effective in monitoring electronic properties of planar, bulk samples are not very useful in the characterization of nm-thin, 3D semiconductor material systems.

Must run, will continue next time...

As some of you who read my blogs could have noticed there is a noticeable educational component in my contributions. My goal is to use 35+ years of experience with semiconductor research and teaching  to help my readers interpret various development and trends in semiconductor science an engineering. It does take long to find on the net many other authors active in this (semiconductors) and other technical and scientific areas.

I truly belive there is a value in such an informal disemination of personal technical experiences made possible due to the  internet. In this sense educational blogging stands on its own merit as opposed to broadly exploited and popular internet outlets designed to share mostly meaningless personal experiences.