To fulfil advanced process control requirements for 1X node production, the semiconductor industry must cope with multiple parallel metrology requirements such as resolution, precision and accuracy enhancement in all directions to answer to new 3D integrated circuit fabrication methods. At the 1D and 2D levels, CDSEM and Scatterometry techniques are the workhorse techniques for production and process control. However, for process control of 3D devices and high resolution patterning such as direct self-assembly lithography, reference metrology is necessary to maintain a global process control uncertainty that is sufficient for production standards. CD-SEM and Scatterometry have intrinsic limitations that limit their utility for these cases, and new characterization methods are needed. Among the industrial reference techniques currently available, TEM and CD-AFM are generally employed to address this issues but both of these techniques have their own limitations for 1X node production. Nevertheless, they are also very useful for engineers to calibrate production CD metrology techniques and for more accurate process window and process development definition at the R&D level. Thus, there is a critical need to develop new technologies that build upon these capabilities while overcoming the limitations.
Proc. SPIE. 8681, Metrology, Inspection, and Process Control for Microlithography XXVII
KEYWORDS: Semiconductors, Scanners, Atomic force microscopy, Scanning electron microscopy, Laser scanners, Photoresist materials, Line width roughness, 3D scanning, Line edge roughness, 3D image processing
We characterized the roughness and side wall morphology of lithographically produced nanostructures of resistmultilayer materials using the recently developed three-dimensional atomic force microscopy (3D-AFM), which has an independent Z scanner intentionally tilted to a certain angle access the sidewall. In order to produce different degrees of Line Edge Roughness (LER) in a given photoresist sample, we systematically varied the Aerial Image Contrast (AIC) at a constant dose for optically imaged resists. We describe herein the effects of AIC on KrF resists that were observed by using 3D-AFM and Critical Dimension-Scanning Electron Microscopy (CD-SEM). High-resolution sidewall images and line profiles obtained by the 3D-AFM technique demonstrate its advantages to characterize the shape and roughness of device patterns throughout the development and pattern transfer process. Taken together, we demonstrate that AFM imaging can identify a trend in Sidewall Roughness (SWR) as a function of AIC effects on photoresist sample, and CDSEM imaging provided supporting evidence to establish the LER trend.
As the feature size of the semiconductor device is becoming increasingly smaller and the transistor has
become three-dimensional (e.g. Fin-FET structure), a simple Line Edge Roughness (LER) is no longer
sufficient for characterizing these devices. Sidewall Roughness (SWR) is now the more proper metric for
these metrology applications. However, current metrology technologies, such as SEM and OCD, provide
limited information on the sidewall of such small structures. The subject of this study is the sidewall
roughness measurement with a three-dimensional Atomic Force Microscopy (AFM) using tilted Z scanner.
This 3D AFM is based on a decoupled XY and Z scanning configuration, in which the Z scanner can be
intentionally tilted to the side. A sharp conical tip is typically used for imaging, which provides high
resolution capability on both the flat surfaces (top and bottom) and the steep sidewalls.
Proc. SPIE. 7971, Metrology, Inspection, and Process Control for Microlithography XXV
KEYWORDS: Metrology, Scanners, Image resolution, Atomic force microscopy, Scanning electron microscopy, Photoresist materials, 3D metrology, Line width roughness, Critical dimension metrology, Line edge roughness
As the feature size in the lithography process continuously shrinks, accurate critical dimension (CD)
measurement becomes more important. A new 3-dimensional (3D) metrology atomic force microscope
(AFM) has been designed on a decoupled XY and Z scanner platform for CD and sidewall characterization.
In this decoupled scanner configuration, the sample XY scanner moves the sample and is independent from
the Z scanner which only moves the tip. The independent Z scanner allows the tip to be intentionally tilted
to easily access the sidewall. This technique has been used to measure photoresist line patterns. The tilted
scanner design allows CD measurement at the top, middle, and bottom of lines as well as roughness
measurement along the sidewall. The method builds upon the standard AFM tip design resulting in a
technique that a) maintains the same resolution as traditional AFM, b) can be used with sharpened tips for
increased image resolution, and c) does not suffer from corner inaccessibility from large radius of curvature