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Improving Yield in TFH Wafer Fabrication by Alan J. Fan, Ph.D., KLA-Tencor Corporation

An automated defect inspection system can provide fast and reliable defect information for thin film head (TFH) wafer fabrication, and eliminate the limited sampling size and inconsistent decision making resulting from an operator’s manual inspection. With the capability of full wafer and full slider inspection, the automated defect inspection system can be employed as an in-line yield and process monitoring tool for TFH wafer fabrication.

Introduction

The ultimate goal of any TFH lab is to produce thin film heads with the highest areal density, while minimizing production costs. This production typically involves heads with small writer and reader track width. Small track width becomes more prone to defects and process variation, so that in-line defect inspections become even more important steps during TFH wafer fabrication. Wafer

Stepper Field

Slider

quick and reliable defect information for in-line wafer yield and process tool monitoring. TFH wafer inspection

Defect inspection for TFH applications presents a different requirement compared to defect inspection in integrated circuit (IC) wafer fabrication. The tens of thousands of devices on a TFH wafer are patterned in a two-dimensional array, with some large spacing and a wide range of topography. Only critical defects falling within a vicinity of the active device are real "killer" defects. A typical TFH wafer fabrication involves many inspection steps, especially after resist development, resist strip, chemical mechanical polishing, plating, etc. The purpose of defect inspection is to either accurately catch a defective or misprocessed wafer for rework or scrap, or quickly and reliably monitor for process tool excursions.

F i g u re 1. Device layout of TFH head array on a typical TFH wa fer. The a rea occupied by the active device ca n b e on ly a fraction of the total waf er are a .

The current manual inspection methodology can no longer provide sufficient and reliable defect information for TFH wafers in process. An automated defect inspection system with high sensitivity to critical defects becomes necessary in any TFH fab in order to obtain

In many TFH fabs, the current inspection method is to have operators manually inspect a pre-defined structure at a defect-prone location for a pre-defined sample size – anywhere from 5 to 20 sites per wafer (Figure 1). A typical TFH wafer can have anywhere from 20,000 to 40,000 heads. Therefore, the limited inspection sample size can seriously impact the reliability and accuracy of the defect information. In addition, the lengthy inspection scheme can delay the response for some process tool excursions. Spring 2000

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