Profilometer: KLA Tencor Alpha Step D-500
The profilometer measures film thicknesses by gliding a 2 micron radius diamond stylus across the surface of a horizontally positioned substrate. The motion of the stylus in the Z axis is measured very accurately, to within tens of Angstroms. An HD video microscope with keystone correction is used to help position the stylus in the desired scan location, with adjustable magnification, lamp brightness, image brightness, and contrast. After taking a scan, a 2-D graphic representation of the profile of the film is shown on the screen. The scan may be leveled between any two desired points on the profile, and then measurements can be taken by positioning two cursors, with one cursor on the bottom of the step, and one on the top of the step. The cursors have a nice averaging feature that allows you to spread out the point across any desired range of data, to calculate an average for that range. This averaging feature is very helpful at canceling out background noise, and it allows for more accurate step height measurements and more accuracy during the leveling procedure. The stylus pressure is digitally adjustable from .03 mg to 15 mg. Lower stylus forces are useful on softer materials (e.g.: soft baked photoresist) to avoid scratching the surface. Higher stylus forces are fine for harder materials such as Si, SiO2, hard baked resist, and cured SU-8. The tip is also less “bouncy” at higher stylus forces which allows for faster scanning speeds. The maximum scan thickness range in the Z axis is 1200 microns. The scan speed is adjustable from .01mm to .4 mm per second. The maximum scan length is 30 mm. The approximately 6” diameter (150 mm) substrate mounting chuck has a manual X and Y stage movement of 20 x 80 mm.
With very small or very lightweight substrates, you will sometimes need to temporarily affix them to something heavier like a full wafer or 2”x 3” microscope slide using double sticky tape, Kapton tape, etc., to keep the substrate from moving during the scan.
A custom-built air spring vibration isolation stage helps absorb and dampen some of the low frequency building vibrations. The smoke colored plastic cover should always be flipped down during an actual scan to help block out background noise.
In order to become a qualified user of the KLA Tencor Alpha Step, you need to follow each of these steps in the order as listed here: