My name is Shawn Coffee and I am the main analyst using the atomic force microscope or AFM metrology technique. I am going to describe a time saving method for microscopic feature identification. This method pertains to all large samples analyzed by techniques that have micron or nanometer sized fields of view including AFM, SEM, TEM, XPS and SIMS.
First, I am going to give a scaling analogy demonstrating the challenge of locating features using an AFM. Ceriumlabs’ Veeco D5000 AFM accepts wafers up to 200 mm in diameter. The AFM’s optical spotting microscope maximum field of view is ~900×900 µm2 or ~0.003 % of the wafer area. Maximum AFM scan area is ~100×100 µm2 or ~0.00003 % of the wafer area. Typical feature size tends to be smaller, but we will use the maximum scan area for this analogy. Let’s use relative size comparisons between a 200 mm silicon wafer and an American football field. Football fields are about 110×49 m2 in metric units. Thus, 0.00003 % of a football field’s area is a 5 cm diameter circle or about the size of a golf ball. Now, envision trying to locate a randomly placed golf ball on the football field? Assume we search for the object with a digital camera taking optical images. Scaled up, the AFM spotting microscope field of view would correspond to only 37×37 cm2 or about the size of a small computer screen. If 5 seconds elapsed during each image collected, it would take over 53 hours to search the entire football field!
It is possible to save the analyst a significant amount time searching for the proper location. The key is through easily identifiable, optically visible references. As an example, a semiconductor silicon wafer has a notch on its circumference. References may be as simple as scratches, bubbles or local discoloration. Surface highlighting using a visible marker (e.g., Sharpie) surrounding the analysis location further simplifies the search. It is not difficult to find features in an area approaching the tool’s field of view scale. It becomes difficult when the search area is significantly larger. Further description is possible (often desired) utilizing images. Analysts can easily relate an optical reference position to the spot for analysis. Images also convey the feature size scale. The image can be either an optical micrograph or a representative diagram. A further step is a brief written description of the analysis spot. A paragraph or two clarifies what is wanted from the analysis.
We at Ceriumlabs understand that the pressure is on to provide results ASAP, and we want to quickly present results keeping you, the customer, satisfied. The quicker our analysts locate a correct analysis spot, the quicker your results will appear. Please help us identify the correct analysis location.