LADA (Laser-assisted device alteration) Introduction

Laser-assisted device alteration (LADA) is a laser-based timing analysis technique used in the failure analysis 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) laser 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)

Failure analysis using Liquid crystal Imaging - Understanding the procedure

Integrated circuits are getting more complicated all the time, necessitating a need for a wide variety of analysis techniques to figure out what's wrong. When so many electronic components are crammed together, the chances of one of them failing is very high. Detecting them is anything but trivial given the fact that the high density makes it challenging to isolate the fault. And this is where failure analysis using liquid crystal imaging comes into play.

Misbehaving components create what we call "hot spots" on the chip. As the name implies, they exhibit a higher temperature than the surrounding areas. It's not easy to detect them since the temperature difference is too low to measure using conventional means. In this article, we see how liquid crystals are used to do the job.

Using Liquid Crystals

Most liquids are isotropic, meaning that there's no order to their molecules. They align themselves randomly and there's no structure to them.

Seebeck effect

Seebeck effect imaging (SEI) uses a laser to generate thermal gradients in conductors. The thermal gradients induced generate corresponding electric potential gradients. This correlation of thermal and electric gradients is known as the Seebeck effect. The SEI technique is used to locate electrically floating conductors.

When the laser changes the thermal gradient of a floating conductor, its electrical potential changes. This change in potential will change the bias of any transistors connected to the floating conductor, which affects the heat dissipation of the device. These changes are mapped to a visual image of the device in order to physically locate the floating conductors.

Original text: http://en.wikipedia.org/wiki/Thermal_laser_stimulation#Optical_beam_induced_resistance_change 

TIVA (Thermally induced voltage alteration)

Thermally induced voltage alteration (TIVA) is an imaging technique which uses a laser beam to pinpoint the location of electrical shorts on a device. The laser induces local thermal gradients in the device, which result in changes to the amount of power that the device uses.

A laser is scanned over the surface of the device while it is under electrical bias. The device is biased using a constant current source, and the power supply pin voltage is monitored for changes. When the laser strikes an area containing a short circuit, localized heating occurs. This heating changes the resistance of the short, resulting in a change in power consumption of the device. These changes in power consumption are plotted onto an image of the device in locations corresponding to the position of the laser at the time that the change was detected.

Original text: http://en.wikipedia.org/wiki/Thermal_laser_stimulation#Optical_beam_induced_resistance_change

OBIRCH (Optical beam induced resistance change)

Optical beam induced resistance change (OBIRCH) is an imaging technique which uses a laser beam to induce a thermal change in the device. Laser stimulation highlights differences in thermal characteristics between areas containing defects and areas which are defect-free. As the laser locally heats a defective area on a metal line which is carrying a current, the resulting resistance changes can be detected by monitoring the input current to the device. OBIRCH is useful for detecting electromigration effects resulting in open metal lines.

A constant voltage is applied to the device-under-test (DUT). An area of interest is selected on the device, and a laser beam is used to scan the area. The input current being drawn by the device is monitored for changes during this process. When a change in current is noted, the position of the laser at the time that the change occurred is marked on the image of the device.

When the laser beam strikes a location which does not contain a void, good thermal transmission exists and the change in electrical resistance is small. In areas containing voids, however, thermal transmission is impeded, resulting in a larger change in resistance. The degree of resistance change is displayed visually on an image of the device, with areas of higher resistance being displayed as bright spots.

Original text: http://en.wikipedia.org/wiki/Thermal_laser_stimulation#Optical_beam_induced_resistance_change

EBIC (Electron Beam Induced Current) Introduction

Electron-beam-induced current (EBIC) is a semiconductor analysis technique performed in ascanning electron microscope (SEM) or scanning transmission electron microscope (STEM). It is used to identify buried junctions or defects in semiconductors, or to examine minority carrierproperties. EBIC is similar to cathodoluminescence in that it depends on the creation of electron–hole pairs in the semiconductor sample by the microscope's electron beam. This technique is used in semiconductor failure analysis and solid-state physics.

VC (Voltage Contrast)

定義:
　　當電子束(SEM)或離子束(FIB)照射電位不同的物質時會有不同二次電子產率(yield),造成影像的亮度不同

原理

當電子束(離子束)掃描過樣品表面時, 會與表面產生非彈性碰撞, 並放射出一些低能(<50 eV)的二次電子

這些電子一般僅能離開表面30nm以內, 利用偵測器前端外加幾百伏特的電壓將這些二次電子吸收,並成像(參考 SEM)

樣品表面的電位會影響二次點子的產率.電位越高放射二次電子量越少,電位越低放射量越多

利用此影像判斷連接線(metal, poly, contact, via)的 open/ short

主動式與被動式 VC:

被動式VC (passive voltage contrast): 此方式僅需將樣品接地-置於載具上(Stage)不須任何外加電源,用於尋找樣品上的短路/開路(open/short) 主動式 VC (Active voltage contrast): 此方法利用Tester將樣品置於操作狀態, 藉由電子束量測IC內部的訊號(參考 probing) 右圖說明其差異: