Spring04 see through haze

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Seeing Through the Haze Process Monitoring and Qualification Using Comprehensive Surface Data Frank Holsteyns, Jan Roels, Quoc Toan Le, Karine Kenis, Paul W. Mertens, IMEC

Haze, the low frequency signal of light scattering on unpatterned wafer, is already accessible on the Surfscan SP1 in most fabs and contains very useful surface information. It can be used as a proxy for other metrology tools to measure thickness, reflectivity, roughness, defects, and can be integrated in SPC tests for equipment monitoring. When combined with defect measurements, it provides additional wafer surface information unrevealed by defect monitoring alone.

Introduction Max LPD

Area

LPD

Min LPD Noise

Haze, the low frequency signal of light scattering on unpatterned wafers is a common technique used in semiconductor production fabs to monitor and qualify a variety of process steps. The information distilled out of the captured scattering light is two-fold: 1) scattering events (light point defects) used to count and size particles, and 2) haze, or the background scattering signal (Figure 1). This study shows that haze, collected as the low frequency signal from a darkfield inspection tool, is a very effective way to gather surface information. The analysis of the haze data can be used as a powerful tool to evaluate process performance concerning defectivity, uniformity, roughness, sealing, etc.

{ Actual Haze

Figure 1. The captured scattered light consists of light point defects (LPD) and the haze signal.

Light scattering tools

In this study, we focus on the use of the KLA-Tencor Surfscan SP1DLS unpatterned wafer inspection tool to extract the haze signal from the tool’s scattered signal. The wafer is illuminated by a laser, with a beam either normal to the wafer surface or oblique (70° to the normal). The scattered light, coming from different defects as well as the background of the wafer surface, is collected 50

Spring 2004

Yield Management Solutions

by two separate channels. The low frequency component of the signal of these channels is given as the haze signal, expressed as scattering power fraction per area of detector to the total incident power (ppm/Star radial).

Haze reference wafers To validate the haze signal, a set of standard calibration wafers was developed on a SEZ spin processor. These wafers, which remained stable over time and were


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