FA usage from laser-assisted tech

At FA applications, there are a lot of chances to localize defect by related laser-assisted techniques just like optical beam induced resistance change (OBIRCH), thermally induced voltage alteration (TIVA), external induced voltage alteration (XIVA) and Seebeck effect imaging (SEI). Describe these techs as below,

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.

FA Critical Tech : EDX (Energy dispersive X-ray spectroscopy)

At FA field, EDX (Energy dispersive X-ray spectroscopy) is one of the most important technology for elemental analysis or chemical characterization of a sample.It is one of the variants of XRF. As a type of spectroscopy, it relies on the investigation of a sample through interactions between electromagnetic radiation and matter, analyzing x-rays emitted by the matter in response to being hit with charged particles. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing x-rays that are characteristic of an element's atomic structure to be identified uniquely from each other.

[Contributor: R. Carpenter] Knock Atoms Off by FIB

In our FA procedure, nano machines or devices require manufacturing very small parts for their construction, and extracting small specimens from them for analysis of structure and composition at the nanoscale level, to analyze performance. Focused Ion Beam (FIB) machining, which is sometimes called FIB milling, has emerged as one of the most useful methods for shaping nanomaterials after synthesis. Near net shape synthesis methods, such as photo lithographic patterning used with chemical vapor deposition, is the other primary synthesis technique. These two techniques are often complementary, and here we illustrate and describe FIB milling.

FIB milling involves removing material from a larger body to make a nanopart or specimen. Examples are nanogears and specimens for transmission electron microscopy cut out from specific regions of interest in electronic nanodevices.

Familiar with Semiconductor Defects

In the FA lab, there are many kinds of defect modes were revealed. The author classify systematically these defects and could be a general idea of  FA engineer.

In this article we take a look at common semiconductor defects or faults which can occur inside a package. Each type of error has multiple detection techniques and the electronic failure analysis method chosen depends on the sensitivity required, the type of chip it is, and whether or not the process is destructive.

The first kind of defect in a semiconductor relates to the materials used. Because of the extreme dependence of the device on the exact makeup of the chip, any variance or impurities in the material will cause it to operate outside the specified range. Detecting these variances isn't trivial and many sensitive methods are used to detect it such as optical emission spectroscopy.

Tip selection for the resonance frequency / the force constant

For C-AFM utilization, tip parameters are most important to determine the image quality and I-V characteristic correctness.

For example, tip choice about tapping mode at our lab, the cantilevers are made from monocrystalline silicon. Therefore the resonance frequency and the force constant are very precisely determined by the geometry of the cantilever requiring no calibration. The thickness of the cantilever is measured with an interferometric microscope. Length and width are measured with an optical microscope.

Resonance frequency and force constant are calculated with these measured values taking the approximate mass of the tip into account. The measurement errors and the simplifaction used in the calculation lead to the following error values for the resonance frequency and the force constant: In the tip sell market, approximately 10% error for cantilevers 450µm in length, Approximately 20% error for cantilevers 125µm or 225µm in length.

Of course, there are many kinds of tip for vary application areas. One could select suitable tip parameters before try these tips.

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: