KEYWORDS: Etching, System on a chip, Image processing, Sensors, Lithography, Semiconducting wafers, Distance measurement, Process control, Transistors, Signal to noise ratio
BackgroundThe self-aligned double-patterning (SADP) process is being used extensively to overcome the lithographic resolution limit in the manufacture of integrated circuits. One use case is fin definition in a fin field-effect transistor. Fin cut layers are applied to modify the fins to the requirements of the device designs.AimThe traditional secondary electron (SE) imaging exhibits a disadvantage in the process controlling the fin cut layers, and fin damage defects were observed. This work aims to improve the monitoring and controlling capabilities for the process quality of fin cut layers.ApproachA specially designed fin cut process flow and a backscattered electron (BSE) imaging technique are applied to check the process quality. The patterns formed through the fin cut etch and the fin structures are identified and measured simultaneously in one BSE image.ResultsBy measuring the edge-to-edge distance, pitch walking (PW) of fins, and overlay (OV), the root cause of the fin damage is revealed. The linear fitting model and third-order fitting model are applied to reduce the edge placement error (EPE). The edge distance protecting the “at risk” fin is enlarged from 5.6 to 11.6 nm. The range of the distance is reduced from 11.6 to 8.1 nm, and the improvement in standard deviation is about 33%.ConclusionsThis work shows the capability of the BSE imaging technique in the characterization of fin cut layers and the potential in process window improvement restricted to fin damage defects.
This Conference Presentation, “A holistic study of edge placement error on fin cut layer in self-aligned double patterning process,” was recorded at SPIE Photonics West held in San Francisco, California, United States.
KEYWORDS: Transmission electron microscopy, Metrology, Scanning electron microscopy, Metals, 3D metrology, Molybdenum, Tin, Semiconducting wafers, Signal to noise ratio, Process control
ABSTRACT The introduction of new three-dimensional (3D) architectures in future logic and memory devices present new challenges for process metrology and control. Where there is a need to recess only one material type out of a superlattice (SL) layer stack, such structures all have in common the fact that the recess is hidden in the stack. Currently, process control in this field heavily relies on expensive, slow, and destructive metrology such as Transmission Electron Microscopy (TEM). In this work, we use the high voltage Scanning Electron Microscope (SEM) technique in combination with the Elluminator® improved Back-Scattered electrons (BSE) technology for better imaging efficiency to demonstrate the ability to measure cavity recess from top-down SEM images. We present case studies both in logic and memory domains. In Horizontal Gate-All-Around (H-GAA) Nanosheet and Forksheet logic devices, the SiGe layer is recessed in a Si/SiGe SL stack. In 3-Dimensional memory devices, we present results on Poly-Si recess metrology in Poly-Si/SiO2 SL stack, Molybdenum (Mo) recess metrology in a Mo/aSi SL stack, and TiN recess metrology in a 3DSCM stack used for memory word line. For the evaluation of the proposed recess metrology technique, several wafers with modulated recess amounts were measured using SEM technology at several high voltage landing energies (LE). BSE signal and advanced image analysis algorithms were used to build a prediction model and quantify the recessed amounts using an edge-based analysis. TEM metrology was used to validate the measurement based on the top-down high LE SEM images. We demonstrate that by using high voltage LE, in combination with enhanced BSE efficiency and advanced image analysis algorithms, we can investigate hidden layers in the stack, identify the recessed material edge, and measure accurately the cavities of interest, thus ultimately providing an inline, non-destructive, and statistically representative metrology solution for such advanced technology nodes. This new application will help chip manufacturers to characterize their processes faster and provide an HVM monitoring and control solution.
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