Improvement of within Wafer Uniformity of Device Parameters by Gradient Temperature Control with Bell Jar Hot Wall RTP

This paper presents a method to minimize cross-wafer threshold voltage variation, specifically radial variation, on device wafers using the inherent characteristics and repeatability of a bell-jar hot wall RTP system. The temperature uniformity of Axcelis´ bell-jar hot wall RTP is controlled by a three-zone temperature gradient. It is possible to change the cross-wafer thermal uniformity from a flat or uniform distribution to either edge-hot, or edge-cold. The settings are characterized and optimized using sheet resistance monitors. It is demonstrated that by optimizing the power levels of the three-zone furnace, an optimized temperature gradient can be repeatedly formed and visualized by convex or concave sheet resistance maps. As results of the radial uniformity tuning, the RTP user can minimize the affect of process variations from other FEOL processes, such as etch or lithography as it is compensated by RTP process. This capability could enhance wafer yield below 80nm technology flash device through better control and uniformity of device parameters