Three challenges seem to be ever-present in the semiconductor industry: speed is never fast enough, reliability is never good enough, and yield can always be improved. These hold true in virtually every application, from computing and communications to consumer electronics and automotive. To achieve the desired improvements, the world’s leading foundries and fabless chip designers have been driving down node size, currently moving below 7 nm. The process of improving yield or reliability includes detailed failure analysis, including semiconductor fault isolation.
Semiconductor fault isolation
While electrical or physical failures are often visible on the surface of a device, marginal failures are less obvious because they are affected by internal issues with voltage, timing, or both. Pinpointing the location of such failures is essential to isolating the cause. For failure analysis lab personnel, successful diagnosis also depends on the ability to access the relevant circuitry without damaging the device or obscuring the defects.
Laser-assisted device alteration
As a general approach, laser-assisted device alteration, or LADA, temporarily changes the operating characteristics of individual transistors, thereby enabling timing analyses that can reveal marginal failures. The typical approach uses a variable-power, continuous-wave (CW) laser operating at a relatively short wavelength (e.g., 1064 nm). The device-under-test (DUT) is put into its normal operating mode, and its output is monitored as the laser targets individual transistors.
Falling short with continuous-wave methods
Unfortunately, this technique has some noteworthy shortcomings. For example, the CW method may create large spot sizes due to n-well effects from neighboring transistors. This can obscure defects and therefore hamper root-cause analysis. Typical techniques may also damage sensitive circuit areas due to excessively high doses of laser energy. Perhaps most significant, the scale and scope of timing analysis is limited when using CW-LADA.
Gaining clarity and maintaining device integrity
A new alternative overcomes these issues and enhances timing analysis. Called time-resolved laser-assisted device alteration (TR-LADA), this method allows failure analysis lab personnel to track down subtle timing issues and debug soft defects in semiconductor devices.
In the failure analysis lab, time-resolved laser-assisted device alteration avoids defect obfuscation and minimizes damage to sensitive circuit areas. Compared to CW-LADA, it also provides higher-resolution semiconductor fault isolation (Figure 1). The result: faster identification of design fixes for marginally failing parts, and thereby improvement of overall yield.
Utilizing dynamic laser simulation for laser-assisted device alteration
Time-resolved capabilities are available as an option for Thermo Scientific Meridian systems: Meridian IV, Meridian 5, Meridian 7, and Meridian WaferScan. All are designed for static and dynamic optical fault isolation on sub-10 nm devices. These systems provide infrared and visible-light EFA, including laser-scanning microscopy; dynamic laser simulation (DLS/LADA); laser voltage imaging (LVI) and probing LLVP); and photo emission. Meridian systems are designed to meet the needs of those who require best-in-class performance and the ability to diagnose wide-ranging failure modes, including parametric failures and those resulting from design-process marginalities.
The time-resolved laser-assisted device alteration option adds a 1064 nm picosecond laser source, timing electronics, controller, acousto-optic modulator (AOM), and digital delay generators. The key software element is a well-conceived user interface that facilitates easy data collection. Additional software elements include a waveform tool as well as control for the laser, timing electronics, and AOM.
Staying ahead of your semiconductor fault isolation challenges
Detailed analysis of semiconductor device failures is essential to improving manufacturing yield, reducing device costs, and minimizing overall end-of-line failures. As node sizes continue to shrink and semiconductor fault isolation becomes more challenging, time-resolved laser-assisted device alteration offers higher resolution in the localization of marginally failing devices.
Jennifer Kopp is a Sr. Product Marketing Manager at Thermo Fisher Scientific.