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Method of Identifying Cracked Wafers

IP.com Disclosure Number: IPCOM000039267D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 127K

Publishing Venue

IBM

Related People

Leas, JM: AUTHOR [+2]

Abstract

Cracks in silicon wafers can be revealed to the naked eye using various thin film liquids to magnify the appearance of the crack. The method allows scanning large surface areas at once to detect submicron cracks. The liquid used depends upon the surface properties of the wafer. For wafers whose surface will wet with water, including as-cut and sandblasted wafers, condensed water vapor works well. For hydrophobic wafers, materials such as alcohol or acetone can be used. Cracks in rough wafers cannot be seen by the naked eye and are difficult to find using microscopy or X-ray techniques. Cracks will appear on rough wafers after they are cooled to the dew point on a cold chuck. Moisture from the air condenses on the rough wafer as a thin film of water.

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Method of Identifying Cracked Wafers

Cracks in silicon wafers can be revealed to the naked eye using various thin film liquids to magnify the appearance of the crack. The method allows scanning large surface areas at once to detect submicron cracks. The liquid used depends upon the surface properties of the wafer. For wafers whose surface will wet with water, including as-cut and sandblasted wafers, condensed water vapor works well. For hydrophobic wafers, materials such as alcohol or acetone can be used. Cracks in rough wafers cannot be seen by the naked eye and are difficult to find using microscopy or X-ray techniques. Cracks will appear on rough wafers after they are cooled to the dew point on a cold chuck. Moisture from the air condenses on the rough wafer as a thin film of water. The surface tension of the water pulls the film away from sharp discontinuities, which causes a 1/4- millimeter-wide dry area, visible to the naked eye, to appear on each side of the crack, as seen in the figure. Cracks that are a fraction of a micron wide can be found with this method. As the condensation of water continues, the layer of water thickens, the dry areas eventually fill in and the crack disappears. If the wafer is reheated, some of the water evaporates, the film becomes thinner and the dry areas next to the cracks will often reappear just before the wafer dries. Either technique of achieving a thin film is suitable for finding cracks. On mirror- polished silicon wafer...