CD inspection by Nuflare NPI 6000 tool

Abstract

Critical Dimension uniformity (CDU) is one of the most critical parameters for the characterization of photomasks. Lately it has been shown that advanced CD (critical dimension) SEM tools and mask processes can distinguish the random short-range CD variation from the global CD signature, which is driven by process and design characteristics. Current electron beam writers can utilize this global CD signature information and correct the CDU of photomasks accordingly. Therefore a detailed knowledge of the signature will benefit strongly photomask CDU. Electron beam writer based signature compensation relies primarily on CD signatures derived from CD SEMs. Here higher spatial resolutions of the signature are achieved only by high cycle times at metrology. The trade off between cycle time and resolution leads to a CD resolution somewhere around one cm. Even then the photomask will have to stay a substantially percentage of the total cycle time at a non-value added process step. In this paper we argue that the solution for this dilemma can be found at a completely different process area - at inspection. We present data showing that the novel CD map feature of the NPI inspection tools enables CD maps in unparalleled resolution in the mm region. This far exceeds CD SEMs by a factor of 100. Also utilization of a tuneable spectrum of different features are not limited to selected CD measurement sites. The CD map is generated in parallel to the traditional defect inspection and works for pre- and post pellicle inspections equally well. To evaluate the method we used a single die layout of a current logic design and referenced all data only to database. Nevertheless, the data presented will demonstrate the excellent repeatability of the CD map measurement and the good matching to CD SEM measurements.