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Sunday, November 27, 2016

#355 Near-surface region

Electronic properties in the near-surface region of any solid, including semiconductors, depart significantly from the same properties in the bulk.  The reason is two-fold. First, the near-surface region of a single crystal semiconductor is disturbed structurally because of the abrupt discontinuity of the crystal structure at the surface. Second, unsaturated broken bonds at the surface are electrically active and unless neutralized over time through interactions with an ambient these so-called dangling bonds  will feature electric charge promoting changes in the distribution of electric charge in the sub-surface region of semiconductor.



Both structural and electrical disturbances in the near-surface region alter key electronic properties of the material. For instance, due to the increased scattering of charge carriers resulting from the defective lattice and electrically charged centers, mobility of carriers µ moving close to the surface is reduced significantly as compared to the bulk. This effect has significant consequences in the operation of transistors used to create advanced CMOS-based integrated circuits.

Posted by Jerzy Ruzyllo at 05:27 PM | Semiconductors | Link

Sunday, November 6, 2016

#354 More on geometrical considerations

Considered in the previous entry nano-confinement is an extreme case of sample's geometry effect on the physical properties of the material. Extreme because at the atomic level confinement quantum phenomena take over control of the behavior of electrons which are now subject to the laws of quantum physics rather than laws of classical physic describing behavior of electrons in the geometrically relaxed solid.


The effect of nano-confinemet and transition to the quantum domain should not let us forget about the case when reduction of material geometry is causing changes of its electronic properties while still subject to the laws of classical physics. For instance, while reducing thickness of semiconductor material, point is being reached at which its electrical resistivity rapidly increases and its bulk properties are no longer defining behaior of electrons.


Exact number defining thickness below which thin-film rather than bulk properties define characteristics of material cannot be given because transition from the bulk to thin-film properties domain occurs at the different thicknesses for different materials and in addition depends on crystallographic structure of material, its chemical composition and others.


In the practical semiconductor devices bulk properties of material rarely come to play when defining device characteristics. It is mostly either thin-films comprising device or the part of the material which is immediately adjacent to the surface that control device operation and characteristics.

Posted by Jerzy Ruzyllo at 09:54 AM | Semiconductors | Link

Sunday, October 16, 2016

#353 Nano-confinement

A concept of nano-confinement and its effect on the properties of solids and operation of solid-state devices is a recurring theme in the disccussion of semiconductor materials and devices these days. This is because with nano-confinement, or in other words atomic scale confinement, different phenomena control properties of solids as compared to their bulk form.


To assign a physical meaning to the term nano-confinement let’s remind ourselves that the diameter of atom depends on the number of electrons it encompasses and varies from element to element from roughly 0.1 nm to 0.5 nm where nm (nanometer) is a unit of length (1 nm = 10-9 m or in other words 1 billionth of the meter). The diameter of silicon atom  is 0.22 nm. As a reference the average size of bacteria is on the order of 1,000 nm, red blood cells about 6,000 – 8,000 nm and only viruses are sized in the low nanometer regime at about 20 nm.

Posted by Jerzy Ruzyllo at 04:22 PM | Semiconductors | Link

Saturday, October 1, 2016

#352 Semiconductor Glossary - book version

It's been quite a while since I got started with an on-line semiconductor glossary. For your information, a book version (2nd edition) of semiconductor glossary has just been published. It is almost twice as large as by now mostly obsolete and unavailable 1st edition and it features some 500 new terms defined as compared to the on-line version.


If interested, you may want to take a look at it on the publishers website. And don't worry about the wrd "Forthcoming" plastered accross its cover. This book IS already available for sale.

Posted by Jerzy Ruzyllo at 04:12 PM | Semiconductors | Link

Sunday, September 11, 2016

#351 UCPSS 2016

The 13th International Symposium on Ultra-Clean Processing of Semiconductor Surfaces, UCPSS 2016, is just getting started in Knokke-Heist, Belgium. As you can see from the symposium program it is giving me an opportunity to elaborate in some more detail specifically on  electrical characterization of as-processed semiconductor surfaces. You may want to take a look at the proceedings volume from this symposium.

Posted by Jerzy Ruzyllo at 10:54 PM | Semiconductors | Link

Sunday, August 14, 2016

#350 Surface Photovoltage (SPV) based method

As mentioned in the previous enrty, Surface Photovoltage (SPV) based method allows characterization  of semiconductor surfaces without a need to process dedicate test devices.  


The SPV method represents non-contact methods of semiconductor surface characterization. It involves the absorption of photons featuring energy higher than semiconductor bandgap which penetrate sub-surface region of semiconductor wafer to the depth dependent on the wavelength of the light used for surface illumination. Resulting generation of electron-hole pairs alters surface photovoltage and allows, by means of Surface Charge Profiling (SCP) methodology  determination of the surface charge, near-surface dopant concentration, as well as surface recombination lifetime. See for instance a paper in which SCP was used to monitor deactivation of boron dopants in the very near-surface region of p-type silicon wafers.

Posted by Jerzy Ruzyllo at 05:31 PM | Semiconductors | Link

Sunday, July 24, 2016

#349 Electrical characterization of semiconductor surfaces

As mentioned in the previous blog methods of electrical characterization provide particularly relevant information regarding chemical/physical condition of semiconductor surfaces.


The methods of electrical characterization of semiconductor surface and near-surface region fall into two categories. The first is based on the use of test devices with permanent contacts (e.g. MOS capacitors or metal-semiconductor diodes) allowing I-V and C-V measurements from which key electronic properties of semiconductor surface can be obtained. Second category involves characterization methods which do not require permanent contact to the surface, and hence, allow measurements of selected electrical parameters of the as-processed surfaces, i.e. surfaces resulting from any given operation without wafer exposure to any additional processing steps.  Methods based on  non-contact Surface Photovoltage (SPV) and temporary contact based Photoconductance Decay (PCD) measurements fall into this category.



Posted by Jerzy Ruzyllo at 09:31 PM | Semiconductors | Link

Sunday, June 26, 2016

#348 Characterization of semiconductor surfaces

With wafer surfaces playing key role in defining characteristics of semiconductor devices and circuits, surface characterization and monitoring processes in semiconductor device engineering are increasingly important. This includes in particular wafer cleaning operations and other surface conditioning steps that need to be closely monitored.


Methods of semiconductor surface characterization that can be used in surface processing characterization and monitoring include (i) chemical/physical surface analysis involving methods such as SIMS, XPS, TXFR, SEM, AFM, (ii) optical methods such as spectroscopic ellipsometry, FTIR and others, and finally (iii)  electrical methods which allow identification of the  surface-related electrically active centers representative of the condition of the wafer surfaces. While not qualitative the last type of methods is of particular interest as they unravel surface characteristics which are directly affecting performance of the final device.  


Posted by Jerzy Ruzyllo at 09:14 AM | Semiconductors | Link

Sunday, June 5, 2016

#347 Semiconductor material engineering - final comments

The recent series of blogs on semiconductor material engineering (blogs #342-346) meant to emphasize how divers outcomes may result from the modifications of chemical make up of semiconductors.Versatility of materials displaying semiconductor properties in this regard can not be matched by any of conductors and only by some insulators.


Due these fundamental characteristics semiconductors will always be a foundation of progress in electronics and photonics.  It seems that this obvious truth needs to be brought to the surface once in a while.

Posted by Jerzy Ruzyllo at 01:50 PM | Semiconductors | Link

Sunday, May 29, 2016

#346 Semiconductor material engineering, part IV

Here is one more example of semiconductor material engineering. This time modifications of the chemical composition of some semiconductors are geared toward alteration of their magnetic properties.


Most of the mainstream semiconductors feature very low magnetic susceptibility, i.e. very small response to the magnetic field. Examples of non-magnetic semiconductors include silicon, germanium as well as gallium arsenide, indium arsenide and others. Some non-magnetic semiconductors when doped with transition metals (e.g. iron, manganese, chromium…) acquire well defined ferromagnetic properties, and hence, turn into magnetic semiconductors. For instance, originally diamagnetic gallium arsenide when doped with manganese (GaMnAs) features significantly increased magnetic susceptibility. Known as dilute magnetic semiconductors these materials will play key role in spintronics.

Posted by Jerzy Ruzyllo at 11:30 AM | Semiconductors | Link

‹‹ ›› is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

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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