Magazine summer00 cmp defect

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CMP Defect Detection and Process TBI Control using the Surfscan SP1 By Katia Devriendt, Paul Mertens, Wim Fyen, Karine Kenis, Marc Schaekers, IMEC, Dale Guidoux, Grant Sergeant, Stephane Robic, Rene Moirin, KLA-Tencor Corporation

The Chemical Mechanical Planarization (CMP) process is now widely used to provide global planarity of layers during the fabrication of integrated circuits. Successful yield management of CMP requires detection of all critical defects in the presence of noise sources such as film thickness non-uniformity within a wafer or process variation within a lot. CMP defects can be separated into two categories; residual slurry particles or other foreign material on the surface, and microscratches or pits in the surface. Both defect types are known to have a negative impact on device yield. In a joint study between IMEC and KLA-Tencor, an experiment was performed to show how the Surfscan SP1TBI unpatterned wafer inspection system can be used to monitor both types of critical defects. Electrical test patterns were generated on CMP wafers to study the correlation of device yield to defect types.

In our experiments, High Density Plasma (HDP) oxide layers were polished using IMEC’s standard oxide CMP process. After cleaning on a scrubber using ammonia on the brushes, the polished wafers were inspected on a Surfscan SP1TBI. As seen in the Surfscan SP1TBI optics layout (Figure 1), the tool has both a normal and oblique incident beam and two collection channels, wide and narrow. The wide and narrow channels were both calibrated to give similar defect counts using Polystyrene Latex (PSL) spheres. On a standard CMP polish and clean, the wafers also exhibited similar Light Point Defect (LPD) counts in both the wide and narrow collection channels. We suspect that the LPDs detected in both channels are primarily surface particles, as we would expect particles to scatter into both collection channels, whereas microscratches or surface void defects should scatter preferentially into only one of the detectors. To confirm this hypothesis, we added or “spiked” the standard CMP slurry with 1.5 µm diameter alumina particles. Another set of HDP oxide wafers were then polished with the contaminated slurry, 72

Summer 2000

Yield Management Solutions

cleaned and scanned on the Surfscan SP1TBI. The wafer scans for each channel are shown in Figure 2. Using an oblique incident “C” polarized beam, the wide channel exhibited a much higher LPD count than the narrow channel. Under review using a CRS confocal laser review microscope, we confirmed that the higher counts Normal Incidence Beam Dark Field Wide PMT

Brightfield Channels SNT Tangential Nomaski DIC

Dark Field Narrow PMT

Ellipsoidal Collector

Lens Collector

Wafer

Figure 1. SP1 TBI optics layout.

Oblique Incidence Beam

SNT Radial Deflection


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Magazine summer00 cmp defect by KLA Corporation - Issuu