July 12, 2011 — Olympus Integrated Technologies America launched the latest 3DIR Metrology and Defect Review System at SEMICON West 2011, booth 1524. The system uses a confocal IR laser scanning microscopy technology for measuring post bond parameters of three dimensional stacked integrated circuits (3DS-ICs).

Greg Baker, president and COO of Olympus Integrated Technologies America, discusses why the company chose to focus its efforts on infrared (IR) metrology for defect inspection of bonded wafers.

The company uses IR because silicon is transparent to near-IR wavelengths. IR microscopy enables acquiring very high resolution, clear images; the key to such images is the laser scanning confocal capability of the microscope — it eliminates out-of-focus layers that are reflected back from the sample, explains Baker. 

Olympus’ 3DIR metrology system measures alignment points at selected die of bonded wafers, stores images and data, and summarizes results. Correlation of overlay alignment offset data to electrical yield provides an early indication of bonded wafer yield. Software tools are provided to display data in the form of vector maps for further review and analysis.

Figure. A pre-bond particle defect is imaged in visible light.	Then relocated and imaged using IR microscopy after wafer bonding. The bonding process has compressed and enlarged the defect to short two lines.

The company integrated the laser confocal microscope into the fully automated metrology tool in partnership with SEMATECH. Three applications that are capable with the resulting tool are: 1) overlay alignment measurements; 2) 3D reconstructions; and 3) defect review (see the figure).

The confocal capability of the microscope allows thin optical sectioning in Z and construction of 3D images of the bonded wafer interface and structures. The 3D reconstructions can be used to create sections in the XZ plane to provide a measurable profile of an imaged structure or feature. Using the confocal capability of the microscope to take XZ measurements at various points on the wafer provides information on the bond interface thickness uniformity.

Using the system’s IR microscope imaging capability, bonded wafers are automatically scanned at low magnification. Images are stitched together to form a single wafer image. When the overlay vector map is superimposed on the scanned wafer image, correlation of many of the failed overlay measurement points to bonded interface anomalies can be seen. Because the wafer scan is done using an IR microscope, the stitched image can be viewed and zoomed for more detail. In addition, any site can be revisited and the image reviewed or rescanned and imaged using the IR microscope with objective magnifications up to 90X and 0.14