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A structure and method to detect circuit opens with improved sensitivity

IP.com Disclosure Number: IPCOM000193412D
Original Publication Date: 2010-Feb-22
Included in the Prior Art Database: 2010-Feb-22
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Abstract

With scaling of feature sizes down starting in 32 nm/22 nm technology nodes, the test structures are becoming increasingly less and less sensitive to open/high resistance defects. This is due to nominal resistance of common test structures such as serpentines are becoming very high with small line width. However, to design smaller structures with lower resistance will increase test time. This poses significant challenges to yield learning. To avoid this hurdle, we are proposing a novel test structure design, test, and analysis method to enable the detection of defects that could not be normally detected.

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A structure and method to detect circuit opens with improved sensitivity

The invention proposes replicates of test structures on a reticle. Instead of analyzing the measurement of individual replicates, measurements are looked in the context of all other replicates. Measurements are normalized for replicate by chip median. Specs are setup for normalized measurement. Replicates with measurements outside the spec are detected as failures.

The test structure is illustrated below using the example of a via chain shown in figure 1. Each chip has several replicates of the via chain shown. Let us assume for example that the chain has 100,000 vias, each via with a resistance of 100 Ohm, with a total nominal chain resistance of 1x107 Ohm.

Fig 1. Example of a replicate

Now suppose the chain had a defect which increased one via resistance to 5x106 Ohm. This changes the total chain resistance from 1x107 Ohm to 1.5x107 Ohm. This change in resistance can be detected using a comparator circuit and is flagged as a failure.

A typical failure detection using a comparator circuit is shown in figure 2. Here BL1 connects to a number of replicates, say for example, 20 via chains. Similarly, BL2 connects to same number of other replicates such as 20 RX serpentines. In figure 2, one side of the comparator is connected to passive array containing via chain (Dut R). The other side of the comparator is connected to a reference resistor with resistance 1.5 times that of the nominal resistan...