Ambient dynamic mode (tapping mode or intermittent-contact mode) AFM imaging has been used extensively for
the characterization of the topography of nano structures. However, the results are beset with artifacts, because hard
tapping of the AFM tip on sample surface usually causes premature tip damage. Through careful study of the
cantilever amplitude and phase signals as functions of tip-to-sample distance, principle of non-contact AFM
operation was discovered to enable high resolution and low tip damage AFM image acquisition [1, 2]. However,
current study discovers that the conventional way of acquiring amplitude and phase versus distance curves gives
erroneous non-contact operating range, because the tip gets damaged during the data acquisition process. A new
technique is developed to reliably map the operating parameters of an intact tip that ensures the AFM be operated
with the correct non-contact settings. Two examples are given to illustrate the successful applications of this new
technique. The first example involves the size characterization of polystyrene latex (PSL) nano particles used for
light scattering tool calibration. The second example is the development of robust recipes for the measurement of
the depth of phase-shift mask trenches.
The objective of this study was to examine the defect reduction effect of the wafer edge polishing step on the
immersion lithography process. The experimental wafers were processed through a typical front end of line device
manufacturing process and half of the wafers were processed with the wafer edge polishing just prior to the immersion
lithography process. The experimental wafers were then run through two immersion lithography experiments and the
defect adders on these wafers were compared and analyzed. The experimental results indicated a strong effect of the
edge polishing process on reducing the particle migration from the wafer edge region to the wafer surface during the
immersion lithography process.
SEM-based defect characterization is a critical technology for wafer manufacturers and others using unpatterned wafers for process monitoring. One of the main drivers of this technology is the need to characterize increasingly smaller defects whose dimensions scale with the shrinking design rules of semiconductor devices. Light-scattering based inspection tools (e.g. KLA/Tencor 6200, SP1) are used to detect defects on the wafer surface and to output a file which contains the xy coordinates of defects relative to the wafer's alignment features. The wafer and defect file are then transferred to the SEM review tool. The defect file is transformed into the coordinate system of the SEM's xy stage in two steps: first an approximate transformation is performed based on the wafer's orientation on the SEM's stage, and then, after several defects have been located, a more accurate transformation is performed using two or more updated defect coordinates. Review of further defects then proceeds and may include high resolution imaging, cross sectioning, and chemical characterization by EDS. This above method can be tedious and somewhat unreliable. It depends largely on the accuracy of the defect file, which contains both systematic and random error. Searching is often required, and it is generally true that the smaller the defect, the more difficult it is to locate by SEM. In this paper, we will discuss the added value and drawbacks of employing a new sample preparation technique which uses precision surface marking and high accuracy defect mapping to minimize the difficulties of SEM-based defect review on unpatterned wafers.
Small-probe analytical tools (SEM/EDX, AFM, AES, TOF-SIMMS, XPS...) are essential for failure analysis in the semiconductor industry. One of the major challenges in this area is in locating the defect within the analytical tool so the defect can be analyzed. The problem is especially difficult for analysis of particles/defects on unpatterned wafers. We have eliminated this problem by developing a new technique called Mark-Assisted Defect Analysis (MADA). The instrument we developed to perform MADA has a robust defect locating capability, and the ability to place micro-sized laser marks in the vicinity of the defect. The marks serve as in-situ landmarks that direct subsequent analysis efforts to the defects location. MADA has enabled numerous analytical techniques to be employed which were previously not possible due to the difficulty in locating the defect within the analytical tool. Examples include the use of multiple analytical techniques for analysis of the same defect, AFM analysis of sub-half-micron particles on bare wafers, SEM/EDX analysis on defects that provide optical contrast but are nearly imperceptible by the SEM, and particle/defect analysis on unpatterned wafers using analytical tools that cannot accept full-wafer samples. In this paper we present an overveiw of the MADA technique and provide several examples of how the technique was employed to solve challenging defect analysis problems on unpatterned wafers.