Specific Process Knowledge/Characterization/Sample imaging

The list of instruments for sample imaging available at Danchip includes 6 optical microscopes , three scanning electron microscopes (SEM's) and an atomic force microscope (AFM). These instruments cover a wide range of applications.

What kind of instrument to use

There is a lot of optical microscopes scattered around in the cleanroom because they are in great need. They are useful if, for instance, you need to

• inspect the quality of UV exposed photoresist when doing photolithography,
• check for particles on wafers that have been processed in the furnaces or the PECVD's,
• check the quality of KOH etched structures or
• generally verify any in batch process.

Using the different options such as bright/dark field, polarizer or transmitted/reflected light one can find a better signal for a specific need. Some of them have a camera that allows you to capture and store images.

One of the advantages of the optical microscopes is that they provide fast and easy accessible information about any sample without any kind of sample preparation. They do, however, also have some limitations. Since the depth of focus is quite limited, especially at high magnifications, one will experience problems when trying to image strucutures that have been etched more than some 10 µm: One cannot focus on both the top and the bottom at the same time. Another disadvantage is the physical limit to the resolution that makes it impossible to image structures below 1 µm.

Both shortcomings of the microscopes mentioned above are addressed if you use a SEM instead. The depth of focus and the resolution of a SEM are at least one order better.

	Optical microscopes	SEM	AFM
Magnification range	25x to 1000x	100x to 500.000x	Maximum scanned area 90x90 µm
Depth of focus	Low	Very high