What is Optical Examination After Deprocessing?

Chemical deprocessing of ICs reveals physical defects related to the circuit's observed failure mode. After each deprocessing step, the die is carefully examined for defects and anomalies potentially related to the failure mode. Optical examination of the deprocessed die involves the use of a high-power optical microscope to locate, image, and photograph defects.

Why Perform Optical Examination After Deprocessing?

Optical examination is performed after each deprocessing step to locate defects related to the device failure.

How is Optical Examination After Deprocessing Performed?

Chemical deprocessing of the IC is first performed as described in Deprocessing. Optical examination is then performed after each deprocessing step by using a high power optical microscope to inspect the die for anomalies. Inspection is begun at a fairly low magnification (50X) and increased up to 500X as necessary to locate anomalies. Based on electrical or other test data, you will know what part of the die to concentrate on.

When is Optical Examination After Deprocessing Performed?

Optical examination after deprocessing is performed immediately following each deprocessing step to examine the die for anomalies. Optical examination is generally performed during deprocessing to ensure that the layer being etched has been completely removed. Optical examination is non-destructive and should be performed prior to SEM imaging, which leaves a carbon residue on areas that have been imaged.

Figures

Figure 1 - Photograph of a masking defect is shown at low magnification (250X). (Photo courtesy Sandia Labs)

Figure 2 - Photograph of a masking defect at higher magnification (1000X). (Photo courtesy Sandia Labs)

Figure 3 - Photograph of a processing defect at higher magnification (750X). (Photo courtesy DM Data)

Figure 4 - Photograph of a mechanical damage is shown at low magnification (100X). (Photo courtesy Sandia Labs)

Figure 5 - Photograph of an epitaxial layer stacking fault at low magnification (100X). (Photo courtesy DM Data)

Figure 6 - Photograph of an epitaxial layer stacking fault at high magnification (750X). (Photo courtesy DM Data)

Figure 7 - Photograph of a particle on a die surface after glass removal. (Photo courtesy Sandia Labs)

Figure 8 - Photograph of a particle beneath the surface shown in Fig. 7 (before glass removal). (Photo courtesy Sandia Labs)

References on Optical Examination After Deprocessing

1. Microelectronics Failure Analysis Techniques: A Procedural Guide, compiled and edited by Ed Doyle, Jr., Rome Air Development Center, Griffiss AFB, NY, and Bill Morris, General Electric Company, Syracuse, NY.
2. John R. Devaney, Gerald L. Hill, and Robert G. Seippel, Failure Analysis, Mechanisms, Techniques, and Photo Atlas, Failure Recognition and Training Services, Inc., Monrovia, CA, 1983.