# US 2019/0318472 A1 · Method for implementing a cd-sem characterisation technique

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- Number: US 2019/0318472 A1
- Document ID: US20190318472A1
- Status: Published application
- Kind: A1
- Application number: 16/469,868
- Filed: 2017-12-12
- Published: 2019-10-17
- Earliest claimed: 2016-12-15
- Assignees: Commissariat A L'energie Atomique Et Aux Energies Alternatives
- Applicants: Commissariat A L'energie Atomique Et Aux Energies Alternatives
- Inventors: Patrick QUEMERE; Jérôme HAZART
- Web page: https://patentgrep.com/patent/US20190318472A1

## CPC

- G06T 7/0004: {Industrial image inspection}
- G06T 7/0006: {using a design-rule based approach}
- G06T 7/001: {using an image reference approach}
- G06T 7/60: Analysis of geometric attributes
- H01J 37/222: {Image processing arrangements associated with the tube}
- H01J 37/28: with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)}
- G06T 2207/10061: from scanning electron microscope
- G06T 2207/30141: Printed circuit board [PCB]
- G06T 2207/30148: Semiconductor; IC; Wafer
- H01J 2237/2801: Details
- H01J 2237/2809: characterised by the imaging problems involved
- H01J 2237/2817: Pattern inspection
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)

## Abstract

A method for implementing a scanning electron microscopy characterisation technique for the determination of at least one critical dimension of the structure of a sample in the field of dimensional metrology, known as CD-SEM technique, the method including producing an experimental image representative of the structure of the sample and derived from a scanning electron microscope, from a first theoretical model based on parametric mathematical functions, calculating a second theoretical model obtained by algebraic summation of a corrective term, the corrective term being the convolution product between a given convolution kernel and the first theoretical model, the second theoretical model comprising a set of parameters to determine, and determining the set of parameters present in the second theoretical model by means of an adjustment between the second theoretical model and the experimental image.

## Claims

### Claim 1

Method for implementing a scanning electron microscopy characterisation technique for the determination of at least one critical dimension of the structure of a sample in the field of dimensional metrology, known as CD-SEM technique, said method comprising:
producing an experimental image representative of the structure of the sample and derived from a scanning electron microscope;
from a first theoretical model based on parametric mathematical functions, calculating a second theoretical model obtained by algebraic summation of a corrective term, said corrective term being the convolution product between a given convolution kernel and the first theoretical model, said second theoretical model comprising a set of parameters to be determined, the first and second theoretical models being a mathematical representation of the structure of the sample in the experimental image;
determining the set of parameters present in the second theoretical model by means of an adjustment between said second theoretical model and said experimental image, the adjustment corresponding to a minimisation of a difference between said second theoretical model and said experimental image.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the second theoretical model is calculated according to the following formula:
Img(x,y)=G(x,y)−C∫∫−∞+∞F(x′,y′)*[G(x′,y′)−G0]dx′dy′
in which:
(x, y) are the spatial coordinates associated with each point of the image along the two orthogonal directions x and y;
G (x, y) is the first theoretical model based on parametric mathematical functions;
Img(x, y) is the second theoretical model obtained by the application of the corrective term;
F(x, y) is the given convolution kernel;
G0 is the background of the intensities present on the experimental image;
C is an adjustment constant;

### Claim 3 (depends on 1)

The method according to claim 1, wherein a primary electron beam scans a surface of the sample according to a TV or raster scan method, the scanning direction being the horizontal direction or x axis.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the convolution kernel is a symmetrical one-dimensional function.

### Claim 5 (depends on 2)

The method according to claim 2, wherein the convolution kernel is a symmetrical one-dimensional function and wherein the convolution kernel is a Gaussian taken along the x axis, said Gaussian having a full width at half maximum proportional to sigma according to the following formula:
Img

(
x
,
y
)
=
G

(
x
,
y
)
-
C

∫
-
∞
+
∞

e
-
(
x
-
x
′
)
2
2

σ
2
*
[
G

(
x
′
,
y
)
-
G
_
0
]

dx
′

### Claim 6 (depends on 1)

The method according to claim 1, wherein the convolution kernel is a two-dimensional symmetrical function.

### Claim 7 (depends on 2)

The method according to claim 2, wherein the convolution kernel is a two-dimensional symmetrical function and wherein the convolution kernel is two-dimensional symmetrical in the directions respectively parallel and normal to the scanning direction of the primary electron beam according to the following formula:
Img

(
x
,
y
)
=
G

(
x
,
y
)
-
C

∫
∫
-
∞
+
∞

e
-
(
x
-
x
′
)
2
2

σ
x
2

e
-
(
y
-
y
′
)
2
2

σ
y
2
*
[
G

(
x
′
,
y
′
)
-
G
_
0
]

dx
′

dy
′

### Claim 8 (depends on 1)

The method according to claim 1, wherein the convolution kernel has a mono-dimensional profile asymmetric along the scanning direction of the primary electron beam or a two-dimensional profile asymmetric along the scanning direction of the primary electron beam.

### Claim 9 (depends on 1)

The method according to claim 1, said method being implemented for a calibration of the CD-SEM characterisation technique, said calibration comprising:
producing an experimental image representative of the structure of a reference sample of which the geometric dimensions are known, said image derived from a scanning electron microscope;
from a first theoretical model based on parametric mathematical functions, calculating a second theoretical model obtained by algebraic summation of a corrective term, said corrective term being the convolution product between a given convolution kernel and the first theoretical model, said second theoretical model comprising a set of parameters, said set of parameters including both the known parameters which describe the geometric structure of the reference sample and the parameters to be determined which describe the instrumental response;
determining the parameters present in the second theoretical model and describing the instrumental response by means of an adjustment between said second theoretical model and said experimental image representative of the structure of the reference sample.

### Claim 10 (depends on 1)

Method for implementing a CD-SEM characterisation technique according to claim 1, said method comprising:
producing an experimental image representative of the structure of the sample and derived from a scanning electron microscope;
from a first theoretical model based on parametric mathematical functions, calculating a second theoretical model obtained by algebraic summation of a corrective term, said corrective term being the convolution product between a given convolution kernel and the first theoretical model, said second theoretical model comprising a set of parameters, said set of parameters including both the parameters to be determined which describe the geometric structure of the sample of interest and the parameters determined according to the calibration according to the preceding claim which describe the instrumental response;
determining the parameters present in the second theoretical model and describing the structure of the sample of interest by means of an adjustment between said second theoretical model and said experimental image.