• Puurunen, Riikka L.
• Utriainen, Mikko

Abstract

Conformality is a core value proposition of Atomic Layer Deposition (ALD) and related thin film processing methods. However, conformality is challenging to measure and quantify and standardized methods do not exist either. This study focuses to identify specific needs and problems in the conformality measurements. The method was a survey and questionnaire. Responders were ALD or other thin film R&D and process engineering experts (N=45), representing academic (N=24) and industry (N=21) and geographically 55% Europe, 25% North America, 20% unknown. All responders considered that it is important or very important to measure conformality, however, only 38% were satisfied with their present measurement methodology. The dominant method is SEM/TEM analysis from microscopic vertical trenches or other high aspect ratio structures. Only few uses alternative approaches (e.g. macroscopic lateral stacks or indirect methods) and those more frequently in academy than in industry. Some responders also state that they try to avoid conformality measurements. Survey showed that the most important attribute was the reliability and accuracy (98% responded 4-5, in the range 1-5) followed by availability of test structures (87%). Lowest success in the present methodology was the speed of measurement (84% responded 1-3, in the range 1-5), followed by cost (71%) and availability of test structures (67%). Responders also described their main challenges. Slow speed is due to tedious (cross-sectional) sample preparation, inaccurate dimensional analyses and multiple sample fractions. Test structures should be comparable to dimensions of real substrates, provide variable 3D dimensions and be available at low cost. Avoidance of breaking valuable wafers was also mentioned. Alternative self-made stacks have challenges e.g. in processing condition compatibility. Other accuracy challenges were low film thickness, inadequate resolution in SEM and missing surface area factor. Responses also pointed out the need of mapping the details on the trench wall/ 3D surface, like morphology, composition, evolution of the film and properties of the film. Significant gap between high importance and low satisfaction of the current measurement approaches leads to conclude that there is a strong need among professionals to get improvements. In this respect, new innovations or joint activities in standardization can support the whole ALD community.

Topics

• impedance spectroscopy
• surface
• scanning electron microscopy
• thin film
• transmission electron microscopy
• atomic layer deposition