By Efrat Raz-Moyal, Gatan

Overview

Delayering samples has become an increasingly complex and difficult process as layer thicknesses decrease, new complex materials are introduced, and demand increases for high throughput. The Centar Frontier offers “hands-free” delayering capability with great precision, repeatable process control, real-time monitoring, and the ability to capture and archive layer images. Delayering with the Centar Frontier can be completed within 45 minutes by any user.

The Centar Frontier uses the following advanced techniques to simplify and streamline the delayering process.

• Predefined or user-configured recipes allow users to achieve repeatable results for any given sample type.
• Exact Angle Control (EAC) lets users increase or decrease tilt and theta polishing angles in 0.003˚ increments, maintaining high planarity and allowing delayering at any location.
• Users can pause to inspect the process at any time, and at each inspection the system will bring up and save a full stitched die image. This auto-stitched image, up to 15mm x 15mm, allows accurate alignment over the whole die. Using the onboard microscope, users can confirm planarity and effective interactive correction.
• Alignment increments of .003 degrees allow users to control the rounding side effect and to delayer die edges and corners.
• Users can select one or many points of interest at any time, and the system will save each image and location. Users can build an archive of images throughout the delayering process, at any selected magnification, and can return to any POI to view its image history.
• Centar Frontier’s functions are controlled through a graphical user interface that gives detailed control of all aspects of the delayering process. Handling is reduced and throughput increased using Centar Frontier.

Recipes

Predefined recipes allow users to get started quickly using default settings. Users can also adjust any of the following parameters to create a new recipe:

• Abrasive
• Time – in one second increments
• Force – in grams
• Direction
• Speed
• Theta and tilt angles – in 0.003-deg increments
• Track position
• Brushing

The default recipes begin with a high removal rate setting, using polishing films such as 3M diamond films. Then the recipe proceeds with low removal rate, soft mineral films such as SiO2, to achieve a high surface quality layer.

Angle Adjustments

Users can control angular adjustments that press toward the polishing plate at the highest point of the sample, in 0.003˚ steps. The adjustments in tilt and theta angles enable a very high degree of planarity between the sample polishing plane and the polishing plate.

A few short iterations are needed initially to align the sample relative to the polishing plate, for true zero degree polishing.

• The theta angle controls the direction of the polishing plane. The theta angle should be set to begin from the opposite side of the spinning plate direction. For example, if a CCW polishing plate direction is being used, the polishing plane should begin from the lower side of the sample and proceed toward the upper side of the sample.
• The tilt angle controls the symmetry of the polishing plane from left to right.

Multiple Points of Interest

At any time during the polishing process, users can select a POI. Its coordinates are saved in an image bank. Users can then return to and capture an image of that POI at later stages in the delayering process. With no limit on the number of POI coordinates you can choose, analysis and comparison of hidden features or features that change between layers is easy.

Following are two examples of delayering steps using the Centar Frontier.

Example 1 – Left-right symmetrical polishing

	Image 1: Here’s a stitched image of the sample before polishing. The front of the sample is at the top, back of the sample is at the bottom. Polishing will use the guideline recipe, with polishing direction set to CCW (the usual case). The abrasive polish direction is from top to bottom (front to back).
	Image 2: After a brief polishing, we view the sample through the onboard microscope. More colors are visible in the bottom left corner, indicating this area is being polished more than the right side. We need to adjust the sample to “press” more on the right side (right tilt), to enable more symmetrical left-right layer removal. We change the angle by 2 right clicks (+0.006˚) and continue polishing.
	Image 3: After another brief polishing interval, we examine the sample again and find that the blue line at the bottom appears symmetrical from left to right. Polishing continues with no further angle changes.

If the target layer is in a low position, it may be necessary to remove a few layers before reaching the target layer. Use coarser grits for bulk removal, then switch to fine polishing film one or two layers prior to reaching the target layer.

ILD colors are good indicators of ILD thickness. Using the onboard microscope, color changes can be used to interpret the progress of polishing direction and the need for angle corrections.

Example 2 – High polish rate in the bottom of the sample

	Image 1: Stitched image of sample; highest point is the colored region. Below this area are several black stripes representing the new layer. Below the stripes is another, lower exposed layer. Adjust angle by 4 clicks up (-0.012˚) to focus polishing on the high point.
	Image 2: The next image shows the highest point has begun to shrink. Fewer stripes are visible, indicating that the area is flattening. Continue polishing with these angle settings
	Image 3: The third image shows the new highest point (center top) after removal of high previous layers. Continue polishing with these angle settings.

Summary of Benefits

Centar Frontier’s delayering process has several distinct advantages over more traditional manual delayering methods:

• High throughput, approximately 45 minutes per sample, with no advance preparation needed for any single layer
• High planarity with 0.003˚ angle adjustment accuracy
• Short training cycle for high yield by any user
• Onboard microscope and color CCD camera for immediate feedback and analysis
• Auto alignment using 3D Exact Angle Control
• Advanced MMI and GUI for ease of use and consistently repeatable results
• Automated stitching and image archiving
• Multiple point of interest (POI) selection and image saving
• Delayering of any location, including edges and corners

   

For product and ordering information on the Centar Frontier, please click here or contact your local Gatan Sales Office.