玻璃晶圆机械性能：与硅的比较

The billion dollar silicon industry is built on the extreme uniformity, chemical, and mechanical strength of perfect crystals of silicon configured in the shape of a wafer for standard  integrated circuit processing. Silicon is an ideal substrate for  creating transistors. Thinning the silicon integrated circuit  (IC) substrate has now become a common process approach  to maintain the trend established by Moore’s law and to meet  the packaging form factor required by consumer applications.  The thinned silicon wafer can be used in a stand alone thin  form factor package, or combined with other thinned silicon  device wafers to create a three dimensional stack IC structure  (3D-IC). A thinned silicon IC wafer is very difficult to handle.  Therefore it generally requires the use of a carrier substrate  attached with a temporary bonding method as an aid to handling.

While it is convenient to use a known silicon wafer as a mechanical carrier wafer during process development activities  for wafer thinning, it is illustrative to consider other alternatives, such as glass wafers. Glass wafers have attributes such  as optical transparency that enable visible inspection and other light-based processing techniques, and innovative forming  processes that minimize or eliminate fabrication steps, for  example. To be considered as a drop in alternative carrier, a  glass wafer needs to have similar mechanical properties as a  silicon wafer. This includes form and fit to travel in and out of  standard fabrication tools plus the basic materials properties  required to act as a carrier.

Figure 1 shows a simplified process for creating a thin silicon  device wafer. Depending on the application, the final device  wafer thickness may be anywhere from about 10 μm to 150  μm. If the device wafer is thinner than 150 μm it is possible to  process the thin wafer through various backside process steps  if the thinned wafer is on a carrier wafer.

There are several methods for accomplishing the temporary  bonding process. Regardless of the temporary bonding method used, to achieve a thinned device wafer with good process  control means the planarity and warp of the complete stack  consisting of carrier wafer, plus temporary bonding adhesive,  plus the silicon device wafer must be carefully controlled.

Fig1

Silicon wafers are very common in wafer fabrication facilities.  A silicon carrier wafer is a very close match to the device substrate wafer. A silicon carrier wafer can be a lower grade wafer and does not have the device specific layers. Thus it may  be a good choice as a carrier wafer in development activities.  However, as the thinning process for 3D-IC transfers into production it is illustrative to consider other alternatives.

Corning has been providing glass solutions for a variety of industrial and consumer applications for more than 160 years.  Among recent applications enabled by Corning’s precision  flat glass process technology is the liquid crystal display (LCD)  substrate. This platform is an attractive option for development to supply alternative high volume substrate material  as a new kind of glass wafer carrier for the semiconductor  industry.