Recent advances in ion beam figuring (IBF) technology are pushing the limits of precision manufacturing. At cosine, this technology is now being applied at industrial scale, enabling customers to achieve thickness uniformity below 10 nanometers (nm) on 300 mm silicon wafers.
IBF is a well-established technique for finishing optical surfaces and has long been used in demanding fields such as semiconductor lithography and synchrotron X-ray optics. In these applications, surface errors of less than a nanometer are routinely achieved. The same level of precision is increasingly important for space-based X-ray optics, where even the smallest imperfections can impact performance.
At cosine, IBF is applied in the production of X-ray grazing-incidence mirrors based on the Silicon Pore Optics (SPO) technology. Each focusing module consists of more than 100 individual mirror plates, making a scalable and cost-effective production process essential. To meet this challenge, cosine uses standard 300 mm silicon wafers as the raw material, enabling automated and repeatable processing within its in-house industrial IBF infrastructure. It can also be applied to for other high-precision wafer-based structures.
Trim300 IBF machine inside of the cleanroom facilities at cosine. The inset shows a photograph of the ion beam inside the processing chamber.
The IBF system at cosine is designed for fully automated 300 mm wafer handling. The chamber on the right side is dedicated to automatic wafer handling, where wafers are taken out of a FOUP (Front Opening Unified Pod) and transferred into the main chamber on the left. In the main chamber, the IBF process is initiated. A focused ion beam locally sputters material from the wafer surface while the wafer is translated in front of the beam to enable material removal across the entire wafer. Once the desired removal function is achieved, the wafer is handled back into the FOUP and a new wafer can be processed.
Measured thickness variation maps of a wafer before (left image) and after (right image) IBF thickness correction.
Achieving deterministic correction requires metrology with nanometer-scale precision. To this end, a white-light reflectometer is used to scan the wafer point by point using near-infrared light. The reflected spectra are analysed by a precision spectrometer to determine the local wafer thickness. The resulting nanometer scale measurement precision defines the ultimate limit of the correction loop.
In a recent demonstration, cosine applied IBF to correct the residual thickness variations of chemical mechanical polished (CMP) wafers that already exhibited excellent uniformity below 100 nm. An initial sample wafer showed a 30 nm peak-to-peak thickness variation, with the typical “Mexican hat” profile characteristic of CMP processes (left side in image 2). After a single deterministic figuring step, the thickness variation was reduced to just 5 nm (right side in image 2), corresponding to an improvement factor of six.
About cosine
cosine is a leading worldwide company in the development of space instrumentation, such as Silicon Pore Optics for astronomy and remote sensing solutions with onboard analytics for Earth Observation and planetary science. cosine combines physics and technology to bring out-of-the-box solutions to its clients. cosine has been developing and delivering innovative measurement systems for space and industrial applications since 1998. The company operates more than 1,000 m2 of cleanrooms and high-tech assembly facilities to build and test the systems we produce for customers at our headquarters in Sassenheim, The Netherlands and at subsidiaries in Berlin, Germany and Benevento, Italy.
