Why are silicon wafers round



10.05.2000 09:42

Recycle wafers

Beate Koch communication
Fraunhofer Society

More than twice as many chips can be produced on 300 mm wafers than on 200 mm wafers. However, the share of material costs in the total production costs increases. A good reason not to throw away test or reject wafers, but to recycle them.

From old to new - what was an everyday rule in grandmother's time applies today to modern high technology. Isiltec GmbH, a spin-off from the Fraunhofer Institute for Integrated Circuits IIS, Components Division, in Erlangen, is building a pilot line for wafer reclaiming of 300 mm silicon wafers together with researchers from the institute. The goal: to make used wafers usable again.

More than twice as many chips can be manufactured on silicon wafers with a diameter of 300 millimeters as on the previous 200 mm wafers. This reduces the price of the chips and increases the price
Yield. The growing telecommunications market in particular has a permanently higher demand for chips - golden times for the semiconductor industry. The pizza-sized silicon wafers have one shortcoming, however: Due to the larger diameter, the proportion of material costs in the total production costs has risen from 8% for 200 mm wafers to around 30%. A good reason not to just throw away test or reject wafers, but to recycle them.

"Wafer Reclaim consists of a number of processes with which we can remove the surface layers from partially or fully processed wafers," explains company co-founder Dr. Hans-Martin Dudenhausen. "After processing, the wafers can be used again in different applications." In order to be able to optimally coordinate the process, it is important to know the life history of the wafer. This provides information about the material layers and layer thicknesses on the wafer surface. First of all, these surface layers have to be removed. Depending on the type of layer, there are different processes for this - from mechanical grinding to chemical-mechanical polishing to etching. The subsequent work steps, which include various cleaning and polishing processes, are identical for all wafers. In the end, the wafer has an exact, almost particle-free surface again.

At the beginning, the wafers are 800 micrometers thick. The reclaiming can be repeated several times. The only restriction: the wafer must not be less than a certain thickness. "Depending on the IC manufacturer, this limit is between 720 and 750 micrometers," explains Hans-Martin Dudenhausen. Only then will the new life for used wafers be over.

Contact Person:
Dr.-Ing. Lothar Pfitzner
Telephone: 0 91 31/7 61-1 00
Fax: 0 91 31/7 61-1 12
Email: [email protected]

Fraunhofer Institute for
Integrated circuits IIS
Component technology area
Schottkystrasse 10
91058 Erlangen, Germany
Press contact:
Dr. Claus Schneider
Telephone: 0 91 31/7 61-1 61
Fax: 0 91 31/7 61-3 90
Email: [email protected]


Additional Information:

http://www.iis-b.fhg.de


Features of this press release:
Information technology, mechanical engineering, economy
supraregional
Research projects
German