Fabricating the nano-circuits employed in next-generation semiconductors demands processes that can repeatedly deliver finer geometries, increasingly complex high-aspect ratio (HAR) plasma-etch patterns, more layers and 3D structures. These processes are now so complex that multiple radio frequency (RF) power sources and matching networks are required to generate and maintain the plasma used for film deposition and the etching of the patterns on the wafers.
Addressing the technical fabrication challenges while maximizing throughput, yield and productivity – and keeping process power as low as possible – means that precise sensing and control of the RF power used in plasma processes has never been more important. This, in turn, demands sophisticated RF conversion technology and RF power sensing equipment that consistently deliver highly accurate measurements, often in real-time.
In addition, manufacturers and customers need the confidence that comes from systems that have been calibrated in line with internationally recognized standards.
As a result of these requirements, semiconductor manufacturers are now seeking advanced sensing solutions that are able to handle the significant demands of the latest RF power processes, and are accredited in accordance with key standards such as ISO/IEC 17025.
Originally developed to allow laboratories to demonstrate technical competence in testing and calibration services, ISO/IEC 17025 is a quality management system that can be applied to organizations and equipment that produce testing and calibration results. Accreditation in accordance with the standard not only gives semiconductor manufacturers and their customers the peace of mind that process measurements will deliver accurate measurements; it also addresses the growing demand for increased traceability.
RF Power Sensing
In many etch and deposition plasma power implementations built around RF power sources and matching networks, the RF generator has often been used as the basis for monitoring and recording the power supplied to the plasma chamber. However, this approach can present a number of issues – issues that become increasingly challenging as the need for more precise and higher power control grows. These include power fluctuations, the impact of temperature and recipe mix, problems caused by distance of the power source from the tool itself, as well as the ability to fine tune power at the point of delivery.
For instance, if the RF source is some distance away from the point of power usage, then there is the potential for significant insertion loss. This loss will impact the actual power that is provided. In theory, it is possible to calculate the loss and then adjust the power source settings accordingly. However, depending on the particular system set-up, insertion loss does not necessarily behave in a linear fashion. As powers increase it can be much harder to estimate the loss.
At the same time, the process can suffer as a result of quantization errors whereby the steps available to the user in the power command system do not necessarily correspond to the exact power delivery needed at the chamber.