Laser-assisted device alteration (LADA) is a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

-based

timing analysis Static timing analysis (STA) is a simulation method of computing the expected timing of a synchronous digital circuit without requiring a simulation of the full circuit. High-performance integrated circuits have traditionally been characteri ...

technique used in the

failure analysis Failure analysis is the process of collecting and analyzing data to determine the cause of a failure, often with the goal of determining corrective actions or liability. According to Bloch and Geitner, ”machinery failures reveal a reaction chain o ...

of semiconductor devices. The laser is used to temporarily alter the operating characteristics of transistors on the device.

Theory of operation

The LADA technique targets a variable power continuous wave (CW)

at specific device transistors. The laser is typically of a short wavelength variety on the order of 1064 nm. This allows the laser to generate photo carriers in the silicon without resulting in localized heating of the device. The LADA technique is somewhat similar in execution to the Soft Defect Localization (SDL) technique, except that SDL uses a longer wavelength laser (1340 nm) in order to induce localized heating rather than generate photo carriers. Both techniques require the device to be scanned with a laser while it is under active stimulation by the tester. The device being tested is electrically stimulated and the device output is monitored. This technique is applied to the back side of the

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

device, thereby allowing direct access of the laser to the device active

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

regions. The effect of the laser on the active transistor region is to generate a localized

photocurrent Photocurrent is the electric current through a photosensitive device, such as a photodiode, as the result of exposure to radiant power. The photocurrent may occur as a result of the photoelectric, photoemissive, or photovoltaic effect. The p ...

. This photocurrent is a temporary effect and only occurs during the time that the laser is stimulating the target region. The creation of this photocurrent alters the

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

operating parameters, which may be observed as a change in function of the device. The effect of this change in parameters may be to speed up or slow down the operation of the device. This makes LADA a suitable technique for determining critical timing paths within a semiconductor circuit. . The laser has differing effects on NMOS and PMOS transistors. In the case of NMOS, the transistor will turn on. For PMOS, however, the effect is to lower the transistor threshold voltage. The effect on the PMOS transistor becomes proportionately stronger as the laser power is increased. The effect is to either increase or decrease the speed of the device being tested. Setup for a LADA analysis involves connecting the device to a test stimulus. The test parameters for operating voltage and device speed are then adjusted to place the device into a state which borders on a pass–fail or fail–pass transition. It is useful to use a tester

Shmoo plot In electrical engineering, a shmoo plot is a graphical display of the response of a component or system varying over a range of conditions or inputs. Origin The origin of the shmoo plot is unclear. It is referenced in a 1966 IEEE paper. Anothe ...

to select the appropriate operating conditions. The effect of scanning the laser over sensitive regions is to trip the device from a pass into a fail condition, or from a fail into a pass condition.

Applications

LADA is useful for confirming or disproving an existing theory for the cause of failure. It may be used to confirm suspected transistor leakage or bus noise. It has also found wide use in localizing process defects as the LADA effect easily modulates transistor characteristics in the same path as the process defect. LADA has been used to analyze failures in

domino logic Domino logic is a CMOS-based evolution of the dynamic logic techniques based on either PMOS or NMOS transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer ...

, state elements in memories and leakage.

References

{{reflist Semiconductor analysis