As device dimensions shrink, the measurement of layer-to-layer overlay is becoming increasingly important. Overlay is currently measured using target patterns fabricated within scribe lines. However, there are residual errors between the measurement values at the scribe lines and the actual values at the circuit pattern regions. Therefore, in-die overlay measurements using circuit patterns are required for precise overlay control. We have developed an in-die overlay measurement method based on SEM images. The overlay is directly measured by comparing a golden image and a test image captured at the circuit pattern region. Each layer is automatically recognized from the images, and the placement error between the two images is determined and used to calculate the overlay. This enables measurement without a specially designed target pattern or the setting up of measurement cursors. In the simulation experiments, the proposed method has linearity and sensitivity for the sub-pixel-order overlay even if the patterns have size variations. The basic performance of this method was evaluated using a defect review SEM. For advanced memory devices, a measurement repeatability of less than 1.0 nm was achieved, and a reasonable wafer map of the overlay was obtained.
As the pattern size shrinkage, it becomes more important to control the critical size of various pattern shapes at
a semiconductor production line. Recently, in a semiconductor process with 20 nm nodes size or less the common
optical and even EB inspection tool have considerable limitation to detect critical physical defects.
From these backgrounds, we have developed the high-sensitivity fixed point inspection tool based on
Review-SEM as the product accomplishment judgment tool for below 10nm size defects on critical size devices.
We examined the basic performance of this inspection tool, optimized inspection parameters including beam
condition and image processing. Then, the defect detection performance was evaluated using various real advanced
memory device containing various critical defects. In this paper, we report these results and show the effectiveness
of this inspection tool to the advanced memory devices.
KEYWORDS: Monte Carlo methods, Scanning electron microscopy, Defect inspection, Metrology, Particles, Sensors, 3D modeling, Inspection, Oxides, Optical simulations
The metrology and inspection of contact hole layers is an extremely complex task. At feature sizes
below 45 nm, an aspect ratio higher than 1:10 is required. SEM metrology and electron beam defect
inspection both face extreme difficulties due to the fact that the secondary electrons from the bottom of the
contact holes are absorbed by the walls and do not reach the detector. In this paper, the pre-charging of a
large area before taking images of the hole was explored. An understanding of the physics involved in
contrast formation and optimization of the system setup may improve SEM imaging. Pre-charge and
imaging were simulated using CHARIOT Monte Carlo software with varying pre-charge and observation
conditions. It was found that at specific parameters in the e-beam setting, image contrast is sufficient for
metrology and defect inspection. The simulations involved high aspect ratio contact holes without defects,
as well as with two types of defects: the remaining under-etched layer at the bottom, and a particle defect
at the bottom. The experimental results of the e-beam defect inspection and CD-SEM of the contact holes
involving the flood beam are presented. The results of the simulation qualitatively agreed with the
measured data.
Dae Jong Kim, Hyung Won Yoo, Chul Hong Kim, Hak Kwon Lee, Sung Su Kim, Koon Ho Bae, Hedvi Spielberg, Yun Ho Lee, Shimon Levi, Yariv Bustan, Moshe Rozentsvige
As design rules shrink, Critical Dimension Uniformity (CDU) and Line Edge Roughness (LER) have a dramatic
effect on printed final lines and hence the need to control these parameters increases. Sources of CDU and LER
variations include scanner auto-focus accuracy and stability, layer stack thickness, composition variations, and
exposure variations. Process variations, in advanced VLSI production designs, specifically in memory devices,
attributed to CDU and LER affect cell-to-cell parametric variations. These variations significantly impact device
performance and die yield.
Traditionally, measurements of LER are performed by CD-SEM or OCD metrology tools. Typically, these measurements require a relatively long time to set and cover only selected points of wafer area.
In this paper we present the results of a collaborative work of the Process Diagnostic & Control Business Unit of
Applied Materials and Hynix Semiconductor Inc. on the implementation of a complementary method to the CDSEM
and OCD tools, to monitor defect density and post litho develop CDU and LER on production wafers. The
method, referred to as Process Variation Monitoring (PVM) is based on measuring variations in the scattered light
from periodic structures. The application is demonstrated using Applied Materials DUV bright field (BF) wafer
inspection tool under optimized illumination and collection conditions. The UVisionTM has already passed a
successful feasibility study on DRAM products with 66nm and 54nm design rules. The tool has shown high
sensitivity to variations across an FEM wafer in both exposure and focus axes. In this article we show how PVM can
help detection of Field to Field variations on DRAM wafers with 44nm design rule during normal production run.
The complex die layout and the shrink in cell dimensions require high sensitivity to local variations within Dies or
Fields. During normal scan of production wafers local Process variations are translated into GL (Grey Level) values,
that later are grouped together to generate Process Variation Map and Field stack throughout the entire wafer.
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