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www.us - tech.com


October, 2023


Advanced SAM Validates Integrity of Electrostatic Chucks


By Del Williams T


he semiconductor fabrication industry now has an advanced new quality inspection tool called scanning acoustic


microscopy (SAM) at its disposal that can dramatically improve the reliability of the electrostatic chucks used to hold wafers dur- ing processes such as vapor deposition and etching. Electrostatic chucks (ESCs) utilize a


platen with embedded electrodes that are energized with high voltage to establish an electrostatic holding force that can be used to “grip” very delicate items such as wafers, foils, or films. ESCs are built in layers, with a layer of screen-printed electrodes sand- wiched between layers of insulative ceramic material. The entire structure is then sin- tered to create a single chuck. With ESCs so integral to the wafer pro-


duction process, one challenge has been the lack of high-resolution tools capable of inspecting multiple layers of sintered materi- al to validate the integrity of the package. ESCs made in this manner can display fluc- tuations or non-uniformities in the thickness of the dielectric layer as well as extremely small cracks and pores that can adversely affect the chuck’s ability to electrostatically secure items. Since ESCs must be constructed and


perform flawlessly to maintain the extreme precision required in semiconductor wafer


production, SAM has become an important new tool for the industry to validate ESC integrity during manufacturing.


Non-Invasive SAM is a non-invasive, non-destructive


ultrasonic testing method. The testing is


microelectronic devices. Now, the same rigor of quality testing and failure analysis is being applied to ensure ESC integrity. “SAM can not only detect fluctuations in


the thickness of the dielectric layer but also the presence of extremely small cracks and pores which could compromise the ESC’s ability to electrostatically secure the sub- strate to the chucking surface. It is essential- ly the equivalent of an X-ray inside the part, so is a comprehensive test method to ensure quality,” says Hari Polu, president of OKOS, a Virginia-based manufacturer of SAM and industrial ultrasonic non-destructive (NDT) systems. OKOS is a wholly owned subsidiary of PVA TePla AG, Germany and offers both manual and automated inspection systems for flat panels, thin plates, circular discs, sputtering targets, and special alloys. For validating the integrity of electro-


OKOS Macrovue 600-P scanning acoustic microscope.


already an industry standard for 100% inspection of semiconductor components to identify defects such as voids, cracks, and the delamination of different layers within


static chucks, advanced, phased array SAM works by directing focused sound from a transducer at a small point on a target object. The sound hitting the object is either scat- tered, absorbed, reflected, or transmitted. By detecting the direction of scattered pulses as well as the “time of flight,” the presence of a boundary or object can be determined as well as its distance. To produce an image, samples are scanned point by point and line by line.


Continued on next page


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