How to Evaluate Roughness Distribution of Wafers by Means of Atomic Force Microscopy

Surface roughness is one of the most important quality parameters for wafer materials in industry and science. Atomic force microscopy is a perfect method to evaluate surface roughness with high precision. An optimized measurement workflow for wafer handling, batch measurement and data evaluation enables analysis on nano-scale with high efficiency.

Introduction

Wafers are the most important raw material in the semiconductor industry. The yearly demand for wafers has continuously increased over the last 10 years from 70 million units in 2010 to more than 100 million yearly units of for the period of 2017 - 2019[1]. The microstructures that ultimately create the functional components like logic devices, memory chips, LEDs or sensors are produced by a complex sequence of coating, etching and cleaning steps which are repeated until the desired 3D structure is finished[2].

The initial surface quality and cleanliness of the wafer is of highest importance during the whole process of micro structuring. The specification of wafers involves parameters for flatness, thickness variation, acceptable number of particles and surface roughness. During the micro structuring a broad variety of parameters is controlled in order to maintain high quality and yield. Typical example are dimensional control after individual process steps, critical dimension analysis, line width- and line edge roughness, defect detection and defect control for lithographic masks and quality control of surface roughness after metallization, cleaning or chemomechanical polishing. Therefore producers of wafers and the subsequent semiconductor industry, but also supplier of equipment like cutting or dicing facilities, instruments for cleaning or polishing or producer of photolithography masks require an efficient and reliable method for surface evaluation.

Atomic force microscopy is the most accurate, nondestructive method for measuring the surface topography on nanometer scale. It creates a 3-dimenional model of the surface which is the base of surface analysis including surface roughness, detection of particles or artifacts and measurement of critical dimensions. 

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