Laser Dark-field Illumination System Modeling for Semiconductor Inspection Applications0 pages

Laser Dark-field Illumination System Modeling for Semiconductor
Inspection Applications
Wei Zhou, Darcy Hart and Rajiv Roy - Rudolph Technologies
Presented at SPIE Optical System Design Conference, Marseilles, France, September 2011

INTRODUCTION

Dark-field defect inspection is an essential quality
control method for the semiconductor fabrication
industry, and it is broadly applied for micro particles
detection in many fabrication processes, from bare
wafer inspection to prior/post litho and etching, to
chip dicing and probing, and to final packaging. Diode
laser-based DF illumination systems (LDFs) play a
critical role in such illumination schemes due to several
key factors compared with broadband light sources:
compact size and power consumption, low cost
relative to high stable output, and most importantly,
the unique optical properties that provide additional
system flexibility for optimization to the specified
applications. A typical LDF illumination system is
shown in Fig 1.

DF ILLUMINATION APPLICATIONS IN
SEMICONDUCTOR DEFECT INSPECTION
INDUSTRY AND BEYOND

Dark Field illumination by definition inputs light on a
2D target, so the specular reflected output is out of the
microscope’s optical collection angle (NA) as shown in
Fig 2.1 and 2.2, and a dark image will be formed on
the detector plan. Only the edge of a z height variation
will scatter the light into more board output angles;
partial light will fall into microscope NA and form
a signal on the detector plan corresponding to the
spatial position on 2D target. Due to the image’s dark
background, a strong signal contrast can be achieved
by a very small amount of input light. Therefore, DF
illumination is a powerful scheme for detecting small
variation in height on a 2D surface.

This paper reviews the significances of LDF to
semiconductor fabrication defect inspection, the
fundamental system model is briefly presented, a
discussion on the trade-off relationship between
the typical system design freedoms and system
performance evaluation criteria, followed by the final
summary section.

Figure 2.1 - Bright-field and dark-field illumination schemes

Figure 1 - Typical LDF system

Figure 2.2 - Dark-field illumination principle
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