07/02/2019

The polished truth: Even the bare wafer has to meet the highest demands.

Sawing, grinding, lapping, polishing - these are the typical processing steps that lead from the raw material "ingot" to high-quality wafers.

Bare wafer production - No sawing without measuring

The so-called ingot, a block e.g. made of silicon or a compound material such as sapphire or GaAs, is the starting product in wafer production. Individual bare wafers are cut with a high-precision wafer saw. In this process, grooves are created whose width and depth must be monitored. This is done with optical multisensor measuring tools, which not only visualizes the saw contour in three dimensions, but also characterizes it quantitatively and metrologically - a task in which classical optical microscopes reach their limits due to a lack of height information. Quantitative process control allows the sawing process to be better controlled so that the specification deviations of the sawn wafers are significantly lower. In addition, the tool wear of the processing machines can be monitored and the behavior of different materials during the sawing process can be evaluated.

Quality standards of the producers are written with capital letters

Manufacturers in the fields of microelectronics, microsystems technology and photovoltaics have high demands on the manufacturing tolerances of the primary product "wafer", since even small deviations can have a negative impact on the quality in the downstream, cost-intensive process steps. The result is a loss of yield as well as reduced efficiency and reliability of the end products. High-quality, partly fully automatic multisensor measuring technology contributes to the monitoring of process tolerances in wafer processing and helps to maintain the required quality standards of the producers.

Process control for wafer thinning and polishing

After sawing, the wafers are further processed using mechanical processes such as grinding, lapping and polishing. The thickness must be maintained over the entire wafer in the range of a few micrometers. Since the wafer is usually doped with a defined doping depth, the grinding process must be adjusted so that the thickness does not fall below a certain level. Especially for thin wafers with lower tolerances, the requirements for accuracy and reproducibility increase.

Thickness deviation is not desired - TTV and Co.

Optical non-contact thickness measurement has established itself here. The same technology is also used to determine the roughness with high resolution. In addition to thin wafers, bonded or taped wafers can also be measured. For wafer thickness and surface measurement FRT relies on a diametrically arranged, calibrated sensor configuration consisting of two non-contact chromatic point sensors. They measure the distance to the wafer at its top and bottom. In this way, the local wafer thickness as well as the thickness variation is reliably determined over the entire wafer surface according to the SEMI standard. The thickness variation in particular, defined by the so-called TTV value, is an indicator of quality in wafer grinding. It allows conclusions to be made about whether the material has been removed uniformly. Only wafers with a very low TTV value can continue to be used for complex tasks.

MicroProf® FE - popular in every front-end HVM fab

A MicroProf® FE is now available for you in our clean room. Come and visit us and experience the MicroProf® FE live.

The MicroProf® FE is designed for the automated measurement of global and local wafer para­meters such as TTV, bow, warp, roughness and waviness, for the quantitative characterization of defects caused by mechanical processing steps, as well as for the artifact-free determinati­on of the nanotopography of 300 mm wafers. It combines the capabilities of the worldwide established MicroProf® 300 with a wafer handling system within an Equipment Front End Module (EFEM) and is equipped with filter units (FFU) to ensure the ISO Class 3 clean room conditions.

The handling unit has a single-arm robot with a vacuum end effector or an edge grabber, two load ports including mapper and RFID reader, pre-aligner etc. The MicroProf® FE is designed for the fully automated measurement with 300 mm FOUPs/FOSBs. In addition, the tool can be configured for processing open cassettes (150 mm/200 mm) and exclusively for 200 mm or 300 mm wafers or as a 200 mm/300 mm bridge tool. In addition to the standard configuration, the tool can be equipped with numerous additional functions, which can also be retrofitted at a later date. Handling can also be performed for non-standard wafers, e.g. highly warped wafers (e.g. eWLB), or thin wafers down to 50 μm thickness. Likewise, further sensors can be retrofitted at a later stage because of the multi-sensor concept.

Thanks to its fully SEMI-compliant measurement solutions, almost maintenance-free hardware components and high throughput, the MicroProf® FE is the perfect workhorse in any front-end HVM-Fab. You can always keep up with the progressive development of technology with reduced investment costs.

Take advantage of this op­portunity! Make an appoint­ment with us and see the MicroProf® FE in action.

Are you looking for further information? You can find it here!

Do you have further questions or comments? Then contact us! Our experts will be happy to help you solve your measuring tasks.