Flatness measurement is a method commonly used for checking the quality of a lapping job or another method of flattening. It is a form of metrology used in the semiconductor industry to test to make sure a wafer or other substrate has reached a level of flatness so that it will be able to work to its most efficient standard. In the semiconductor industry, components sometimes need to be at or below a very small amount of micrometers, so being able to make sure the device or component has been flattened evenly and to the right height is ideal.

In lapping, two surfaces are rubbed together with an abrasive in between them, one to be smoothed out and used as the main substrate. This technique can either take place in one of two forms, one of which is grinding, in which a material like glass is then rubbed against a piece of iron to create conchoidal fractures, which are then removed by the abrasive. The other form of lapping is softer, and is used to cut a harder material. The abrasive crosses through the softer material so that it may cut the harder one. Both of these techniques, however, are bound to result in inconsistencies or errors due to their rather blunt technologies. For this reason, flatness measurement is necessary to make sure that the substrates are perfectly smooth.

In flatness measurement, there are different tools that can be used. One of the more common techniques is to use a height gage, which is placed on a surface plate in order to measure the substrate. It must be setup upon three stands in order to establish a minimum variation. This assures that the measurement will not be in error. This method is then able to measure how parallel the substrate is once it is opposite it. This is only capable of measuring to within little under a millimeter of an inch, however, and thus may not be the best tool for semiconductor flatness metrology, which often may be in increments far smaller than that.

Though not all flatness measurement is used to examine parts that have exclusively undergone lapping, a great technique for measuring them is the use of a monochromatic light. The interference and reflection are measured in this way. An optical flat is positioned on the surface of the lapped object. The transparency of this flat allows light to pass through, so when the monochromatic light is shone from above, the light reflects directly off of it. A contour map becomes visible from the light bands as this occurs. Now the flatness of the object can be easily measured.

Flatness is critical to microelectronic components, especially in the semiconductor industry. Without a certain degree of flatness, the substrate will not be able to operate correctly, so being able to measure and assure that the right flatness has been reach is essential for semiconductor engineers. As such, flatness must be carefully checked and cannot be overlooked. 

Flatness measurement is great for checking the results of lapping and other flattening methods. It is integral that the correct level is reached and that the object or substrate being measured is not at all slanted. This could be detrimental to the overall device, as functionality and efficiency would be down. Flatness measurement assures that few defects are going to occur due to a certain component and simply keep companies from sending out components that are not yet ready to be used due to improper lapping. This technique is a useful method before sending out products like wafers or other surface-important products to be used.