• Riedel, Stefan
• Gao, Feng
• Kia, Alireza M.
• Puurunen, Riikka L.
• Utriainen, Mikko

Abstract

Atomic Layer Deposition (ALD) technology enables manufacturing of<br/>conformal thin films into such deep microscopic trenches and cavities that<br/>the film characterization becomes a true challenge. In ALD applications<br/>these 3D microstructured substrates are typically vertically oriented high<br/>aspect ratio (HAR) structures. Monitoring and control of conformality relies<br/>predominantly on cross-sectional sample preparation and SEM/TEM<br/>characterization. This approach has several challenges, e.g. need to break<br/>the wafer, seeing only thin slice, cleavage plane inaccuracy, multiple<br/>repeated samples to get reliable data and long response times.<br/>A potential approach to circumvent the challenges is a MEMS-based allsilicon lateral high aspect ratio (LHAR) test structure, PillarHall® developed<br/>at VTT [1-2]. The LHAR test chip is IC cleanliness proven and thus<br/>potentially compatible to any cleanroom environment. This study focuses<br/>to research questions: How reliable and accurate is LHAR test in 300 mm<br/>wafer manufacturing environment and, especially, how does it compare to<br/>vertical HAR structures.<br/>The LHAR Test Chip (LHAR3 -series, AR range 2:1 - 10000:1, 500nm gap<br/>height) was employed for the first time on the carrier wafer in 300 mm<br/>wafer ALD process (Jusung Eureka 3000) in Fraunhofer IPMS. The ALD<br/>process was foundry’s default ZrO2/Al2O3 laminate process, 22 nm, carried<br/>out in two process variation runs (A=optimized for 3D, B=planar) at same<br/>temperature and cycle numbers. In the same run was employed LHAR and<br/>vertical trench test structures (AR 20:1). Conformality of both structures<br/>were analyzed by SEM cross-sections, with appropriate sample<br/>preparations.<br/>Findings show that conformality in LHAR is comparable to vertical HAR<br/>within accuracy limits of step coverage metrology within the comparable<br/>AR range. Furthermore, in this study, higher aspect ratios in LHAR test chip<br/>shows significant differences between the process variations while in VHAR<br/>they are small. Therefore, even optical microscope metrics from LHAR<br/>provides fast relative insight to the process variations and can be utilized in <br/>monitoring. LHAR enables also access to gain more detailed compositional<br/>information on the trench wall e.g. by ToF-SIMS, which is under<br/>examination and a topic of further studies.

Topics

• impedance spectroscopy
• scanning electron microscopy
• thin film
• transmission electron microscopy
• selective ion monitoring
• atomic layer deposition
• ion chromatography