Industrial Microscopes

Microelectronics and semiconductor wafer manufacturing are believed to be among the fastest evolving technology industries in the world today. Wafer sizes typically are 200 mm to 300 mm while critical dimensions are shrinking to 0.09 um and smaller in size. As the size of discrete devices continues to be reduced while device density increases, the need for fast, accurate, and very flexible metrology and inspection tools in the microelectronics industry increases. Back in the early 1980s, semiconductor inspection was performed primarily by brightfield optical microscopes and with automated detection tools. The adaptation of automated detection tools led to the systematic control of increasingly smaller defects. The smallest detectable defect using these automated tools fell to below the 0.30-micron mark during the 1990s. As semiconductor design rules decreased, it then pushed the requirements for defect inspection into the domain of the Scanning Electron Microscope or the SEM. These instruments were able to easily resolved defects of 0.25 um and smaller. However, the increase in resolution came at a price in speed and flexibility. Likewise, SEM inspection took longer due to time consuming manual sample preparation. The delay in the manufacturing environment was often too long and as a result, a bridge tool was developed that was based on confocal imaging.

The older confocal imaging microscope provided many of the speed advantages and ease-of-use capabilities found on the standard optical microscope. However, the new advantage was the ability to create 3D images based on the unique confocal imaging technique that enables image slices to be stacked. This allows the creating of high contrast images and improved resolution down to 0.18 microns at a wavelength of 450 nm. However, as the push towards the current state-of-the-art semiconductors continued, even this fast and efficient confocal technology was not enough and the most demanding users were forced to resort to the current generation of powerful SEM inspection tools and laser based confocal microscopes with 408nm lasers. As the need to increase circuitry complexity while increasing wafer size grew in the semiconductor industry, the need to look below the surface at the underlying layers for broken leads, faulty connections, and other defects grew correspondingly. No inspection technique was available that could penetrate the surface of the wafer without causing damage to the wafer or packaged device. The only way to perform an inspection was to destroy a wafer - to break it open, polish the edges and take a look at it. For encapsulated devices, it usually meant removing layers of material with acid or other expensive and time-consuming processes. In all cases, it meant destroying expensive samples, training technicians to destroy and prepare samples correctly so that they weren’t considered useless and then using valuable time preparing samples for insertion into a SEM vacuum chamber or even under an optical microscope.

In response to this important need for subsurface imaging, enhance laser scanning techniques have been developed over the past five years. IR laser confocal imaging was introduced. The semiconductor industry in particular is believed to greatly benefit from the use of infrared wavelengths. This is because confocal IR rays easily pass through silicon wafers. This enables the manufacturers to inspect the many layers of a wafer without destroying the expensive sample. With the incresing use of flip chip technology, confocal IR microscopy technique has been gaining popularity to visually inspect for pattern or leak dams chips after electric testing and to measure gaps and alignment between the chip and its interposer. Using IR microscopy, the manufacturer can quickly identify areas that need to be further analyzed by a scanning electron microscope, saving expensive SEM operation and time of analysis. For wafer-level, chip-size packages, IR microscopy is suited ideally to non-destructive inspection for delamination, deformation and the pattern’s fusion and erosion by resin expansion and contraction after heat and humidity testing. What makes confocal IR laser microscopy so attractive to the microelectronics manufacturing industry is its ability to bridge the between standard optical microscopy and scanning electron microscopy. Also, one of the key benefits of the IR confocal technique is its ability to perform three-dimensional measurements within the device. This allows for fast and repeatable measurements that provide quick solutions to critical alignment problems with multi-layer devices as well as bonded devices. In short, the confocal IR laser microscopy is the right technique at the right time for wafer manufacturers facing increasingly complex chip topographies, rising costs, and lowering margins. The IR confocal technique enables manufacturers to perform fast, flexible, accurate, and cost-effective inspections and measurements in real time without the time and money costs associated with scanning electron microscopy.

This entry was posted on Thursday, May 24th, 2007 at 3:29 am and is filed under Industrial Microscopes. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.