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Texas Instruments evaluates KLA-Tencor’s new UBB wafer inspection technology At the October 1997 Yield Management Seminar held in Austin, Texas, Texas Instruments’ MSTC/DP1 development fab presented the results of a three-month study comparing the performance of KLA-Tencor’s 2138 ultra-broadband (UBB) inspection system with the earlier 2135 and 2132 inspection technologies. Results showed that the 2138 consistently provided higher defect capture than the older tools, in one case even when utilizing larger pixel sizes.
New UBB Technology
Objectives and Methodology
The KLA-2138 features an ultrabroadband illumination source, compared to the narrow-band (NB) source of the 2135 and 2132. The UBB’s wider range of wavelengths enables the system to optically average out the effects of color variation caused by non-uniform film thickness. This increases signal-to-noise for higher sensitivity to all types of defects. Defect sensitivity and capture on the 2138 are further improved with KLA-Tencor’s Segmented Autothreshold Technology (SAT), an image processing technique that segments the wafer image based on the gray level signature of the pattern. SAT algorithms dynamically set separate thresholds for each segment, rather than a single threshold for the entire image, maximizing defect capture and minimizing nuisance defect counts.
The objective was to compare the performance of the 2138 UBB technology to the 2135 NB technology on two memory levels and three logic levels. Because the 2135 at DP1 did not have the SAT algorithm, a 2132 was added to the comparison which did have the SAT feature. Table 1 shows the comparisons run at each level. During the experiment, one person from TI was assigned to each level to ensure classification consistency. 100% of all defects on all wafers were classified. In addition, all inspection tools looked at exactly the same area on the wafer. Finally, KLA-Tencor application engineers created and optimized all of the recipes, while TI personnel ran the wafers, classified all the defects and created all of the results files.
• Utilizing the 0.62 pixel size and SAT, the 2138 detected more defects than the 2132 using 0.39 pixel size and SAT, resulting in a throughput improvement. • For memory levels, the 2138 always had greater defect counts than the 2135 using a combination recipe test: 0.25 µm pixel size for array mode, and 0.39 µm pixel size for random mode. 2138 0.39 SAT 2138 0.62 SAT 2132 0.39 SAT 2132 0.62 SAT
Particles
Residue
Metal Defect
Blocked Etch/ Undercut
Figure 1. Defect summar y for the comparison results at metal 3 etch.
circle RS#012
Expected Benefits Given these advantages, the DP1 evaluation team expected to see the following benefits from the 2138: • Improved signal-to-noise • Improved sensitivity on wafers with color variation • Capture of unique defect types vs. the 2135 • Ability to use large pixel sizes on the 2138 vs. the 2135/32 for improved throughput
P Probe Marks
Results Following is a summary of some of the results obtained by Texas Instruments: • The 2138 always found more defects than any other 21XX tool for the same pixel size.
Experimental Methodology Device
Level
2138
LOGIC
METAL 3 ETCH
0.39 SAT 0.62 SAT
LOGIC
VIA 1ETCH
0.39 SAT 0.39 AT
LOGIC
GATE ETCH
MEMORY SNET
Summer 1998
Table 1
2135
2132 0.39 SAT 0.62 SAT 0.39 SAT
0.39 AT
0.39 SAT 0.39 AT 0.62 SAT
0.39 AT
0.39 SAT
0.25 ARRAY 0.39 AT
0.25 ARRAY 0.39 AT
0.62 SAT
Yield Management Solutions
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