Patrick D. Kinney

Locating defects on wafers for analysis by SEM/EDX, AFM, and other microanalysis techniques

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.

New sample preparation method for improved defect characterization yield on bare wafers

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 wafers 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 SEMs xy stage in two steps: first an approximate transformation is performed based on the wafers orientation on the SEMs 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.

Microscopy and spectroscopy characterization of small defects on 200mm wafers

The standard method for the detection and mapping of small particles on 200 mm unpatterned wafers is light scattering. The standard approach to determining what these particles are, and their origin, is to re-find them in a full wafer SEM and rely on SEM/EDX for analysis. At very small particle sizes (below 0.2 microns) the light scattering location inaccuracies make it hard to re-locate the particles in SEM and EDX can have difficulty because it is not a small volume technique. In addition EDX often does not have enough characterization power to lead to a root cause determination. A number of 200 mm analytical alternatives have become available since the first conference in this series two years ago. Between them they provide better small volume and surface sensitivity, plus chemical and molecular information. These are: other modes of optical microscopy combined with wafer marking, AFM, SAM, FIB, and TOF-SIMS. We have evaluated all these using real defect situations on full wafers. A review of their cap...