Researchers from the National Institute of Standards and Technology (NIST) have uncovered a serious error in an industry-standard calibration technique. This error has the potential to cause microchip manufacturers to lose around one billion dollars on a single fabrication run. Scientists believe that this problem will grow exponentially as chip designers continue to increase the number of features while reducing the available space.
The microchip error happens during the process of measuring extremely small flows of exotic gas mixes. These small gas flows occur when chemical vapor deposition (CVD) happens. This process takes place inside a vacuum chamber; ultra-rarefied gases move across a silicon wafer, allowing them to leave behind a solid film. This method of fabrication is used in all kinds of high-performance microchips, including those containing up to several billion transistors.
CVD creates a complicated 3D structure by depositing layers of molecules or atoms. There is a complementary process to this creation called plasma etching. Plasma etching uses small flows of exotic gas as well; the gas is utilized to remove small amounts of silicon from the surface of the semiconducting materials. This allows the exotic gases to produce tiny features.
A key component of this work is the amount of gas injected into the chamber. If it’s not absolutely precise, the results could spell a significant loss to microchip creators. A device called a mass flow controller (MFC) carefully regulates the levels of gas inserted into the chamber. MFCs are responsible for ensuring the deposited layers are of the perfect size and depth. If the measurements are even slightly off, the chips will end up with incorrect layer depth — rendering them useless.
Nanofabrication is a pricey endeavor. Each facility costs several billion dollars, meaning it’s not exactly cost-effective for most companies to regularly adjust and alter plasma etching and CVD. Most facilities depend on the MFCs to control gas flow. MFCs are usually calibrated using the ‘rate of rise’ (RoR) method. The RoR method takes multiple measurements of pressure and temperature over time while the gas fills a collection tank through the MFC.
Unfortunately, as the new research confirms, these measurements are not consistent across the board. Erroneous temperature values can compromise the entire production, resulting in useless microchips and potentially billions in wasted funds.
Scientists are working to create a uniform solution that will ensure a precise flow of vapors and help to streamline the microchip fabrication process.