Optical displacement metrology using alternating direction Moire

Kyoichi Suwa,Koji Kaise,Hiroki Tateno,Nobutaka Magome

doi:10.1117/1.oe.53.8.084101

Kyoichi Suwa, Koji Kaise + Show 2 more

Open Access

https://doi.org/10.1117/1.oe.53.8.084101

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Abstract

We develop a new double exposure Moire method for an optical registration metrology system in photolithography. Our method enables us to achieve at least a factor of 10 improvements in precise displacement metrology using a conventional optical sensor. We utilize a new registration mark printed to the photoresist on a bare silicon wafer using a double exposure of the gratings. The mark consists of two types of Moire with opposite phases. The two types of Moire are oriented in alternate directions. Displacement is measured from the distance between the positions of the two types of Moire in analogy with the conventional registration method. This concept is called alternating direction Moire. Performance is experimentally confirmed using an i-line wafer exposure apparatus. Precision is improved by up to 32 times as compared with the conventional method and can be applied to other Moire metrologies.

Highlights

A wafer aligner is a semiconductor exposure apparatus that aligns a wafer to a mask for each exposure field
Using some form of photolithography registration metrology, optical registration metrology system (ORMS) measurements are possible during the alignment process using wafer alignment optics installed in the wafer aligner
Experiments are performed to validate the alternating direction Moire (ADM) precision of the 1-D alignment optics equipped with an exposure apparatus and a laser step alignment (LSA) measurement system installed in a Nikon NSR-1755iA (NA 1⁄4 0.50, illumination NA 1⁄4 0.30), which is an i-line exposure apparatus

Summary

Introduction

A wafer aligner is a semiconductor exposure apparatus that aligns a wafer to a mask for each exposure field. Using a stage that sequentially moves field by field, the exposure apparatus can expose a field with a series of alignment sequence steps until the entire wafer surface is exposed. An optical registration metrology system (ORMS) measures the amount of exposure displacement error. Using some form of photolithography registration metrology, ORMS measurements are possible during the alignment process using wafer alignment optics installed in the wafer aligner. These measurements are done with an independent ORMS, which is a commercially available tool. We define ORMS to measure the photoresist marks on bare silicon wafers only. ORMS will be used mainly for analysis of machine performance, which is very useful for wafer aligners

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