Optical wafer metrology sensors for process-robust CD and overlay control in semiconductor device manufacturing

Abstract

This paper presents three optical wafer metrology sensors that are used in lithography for robustly measuring the shape and position of wafers and device patterns on these wafers. The first two sensors are a level sensor and an alignment sensor that measure, respectively, a wafer height map and a wafer position before a new pattern is printed on the wafer. The third sensor is an optical scatterometer that measures critical dimension-variations and overlay after the resist has been exposed and developed. These sensors have different optical concepts but they share the same challenge that sub-nm precision is required at high throughput on a large variety of processed wafers and in the presence of unknown wafer processing variations. It is the purpose of this paper to explain these challenges in more detail and give an overview of the various solutions that have been introduced over the years to come to process-robust optical wafer metrology.

Information-Efficient Metagrating for Transverse-Position Metrology

“…One particular important research area in optics is the development of sensitive metrology methods to measure a very small displacement around a certain point [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. This problem is fundamental to pushing the limits of fields such as interferometry [7][8][9][10], metrology [6], and superresolution microscopy [1][2][3][4]. Measuring a small displacement amounts to a parameter-estimation problem in the presence of measurement noise, which can be due to either imperfections of the setup or, more fundamentally, the intrinsic fluctuations due to photon shot noise using coherent light, which scales as 1/ N probe , with N probe being the number of photons used to probe the change in position per unit time.…”

Retrieval of the complex-valued refractive index of germanium near the M4,5 absorption edge

“…The refractive index is intimately tied to the electronic structure of solids; in the visible wavelength regime, it reports on transitions from the valence to conduction band, while in the extreme ultraviolet (XUV) or x-ray regimes, it probes transitions from core states into the conduction band. The current industrial development of XUV lithography at 13.5 nm will eventually require the extension of existing optical metrology techniques into the XUV [2,3]. Such techniques require knowledge of the broadband complex refractive index.…”

Asymmetric Excitation of Surface Plasmon Polaritons via Paired Slot Antennas for Angstrom Displacement Sensing

“…The interferometric method has been well developed and widely applied to detect relative phase differences introduced by tiny longitudinal displacement [2]. Additionally, high-precision measurement of transverse displacement is also challenging and greatly demanded for the development of nanotechnology, such as single molecule tracking [3][4][5][6][7] and nanoscopy [8], as well as overlay metrology for the semiconductor fabrications [9,10]. Developing a highresolution optical ruler [11,12] is a direct optical metrology for the measurement of transverse displace, however, suffering from the requirement of an ultrastable laser.…”