edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 2 12 generally etches insulators faster than conductors, leaving the underlying metal contact lines intact (Fig. 2). 2. Enhanced etch with diiodine (EE I2) accelerates the removal of aluminum (Al) layers, but it also corrodes copper (Cu) layers. As a general note, Cu should not be exposed to iodine. When applying chemistries, nozzle location is important (Fig. 3). In practice, the best choices vary by application. As a general note, gas nozzles should be placed farther away from the region of injection if greater contrast is needed. One reason: close placement can hinder the production of secondary electrons and reduce image quality. Careful consideration of four more parameters will enhance success rate: 1. Finding the proper ratio between oxygen and the insulator deposition (IDEP) chemistry 2. Optimizing the ratio of oxygen source (e.g., O2 or H2O) and the precursor 3. Establishing the right flow rate, neither too much nor too little 4. Optimizing pixel density and dwell time to maximize image resolution As a rule of thumb, the smallest possible dose is best and it should be noted refresh rate, retrace times, and raster pattern times should be taken into consideration. ESSENTIAL FIB PARAMETERS When working with a FIB-based circuit-edit system, the key factors are beam current, GIS chemistries, imaging parameters, and end points. These key factors are determined based on the patterning parameters of pixel density, thickness, visible end-pointing, and graphical end-pointing. A FRAMEWORK FOR KNOWING WHEN TO STOP Knowing when to stop depends on tool capability, user experience, and advice from device experts. For example, what is the right depth for an N-well for a given process, device, or architecture? Graphical end-pointing can help determine when to stop during small via edits. In terms of user experience, this is where it becomes necessary to turn science into art. Mastering the “art” certainly comes with practice. The “science” requires gaining familiarity with the end-point detection system built into systems (Fig. 4). The detection system provides a visual indicator of what’s happening by measuring the secondary electrons that are emitted from the edited material. Note that SiO2 Fig. 3 Precise chemistry delivery is essential to making exact cuts and achieving uniform delayering, and the use of advanced gas-injection systems ensures optimal interaction of the chemistry, the beam, and the device. Fig. 2 The IEE process generally etches insulators faster than conductors, leaving the underlying metal contact lines intact. Fig. 4 Art and science meet to create an N-well with the right depth.
RkJQdWJsaXNoZXIy MTMyMzg5NA==