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Sunday, September 7, 2014

#303 Wafer thickness

Just to make it clear, my comment in the previous blog regarding increasing thickness of the substrate wafers needed to assure adequate mechanical stability of still larger wafers, applies to advanced IC manufacturing using high-quality single-crystal silicon wafers.


Considering exuberant cost of an advance IC design, masks, manufacturing processes etc., the cost of somewhat more silicon being used to make the wafer thicker is almost marginal. At the same time, thickness of the wafer has basically no effect of the operation of an integrated circuit formed within very shallow region at the wafers top surface.


Considerations regarding thickness of the substrate wafers in photovoltaics, in other words substrate wafers used to manufacture solar cells, are drastically different  (well, yes, they are square rather than circular ones used in IC manufacturing, but it’s not a point).


First, in the case of solar cells the cost of material is the major portion of manufacturing costs. Any reduction of the cost of material resulting from using thinner substrates, i.e. less material, translates directly into the decrease of the cost of energy generated by solar cells. From this point of view, substrate wafer, Si for instance, should be as thin as possible. Second, thickness of the substrate wafer matters also because it affects the efficiency of conversion of solar energy into electricity by impacting light absorption characteristics of the material. Except that in this case thinner is better only up to certain point and making wafer too thin will actually hurt cell’s performance


Considering all of the above (and making a long story short), an optimum thickness of Si substrate wafers used in photovoltaics should be somewhere around 50 µm. As the thinnest wafers used now to manufacture solar panels are about 150 µm thick, photovoltaics industry is faced with significant challenges on its way to the sub-100 µm wafer thickness regime. It’s not easy to manufacture such ultra-thin wafers and it’s even more difficult to handle them during subsequent solar cells manufacturing processes due to their extreme fragility.




Posted by Jerzy Ruzyllo at 05:11 PM | 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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