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SEMI P36-0600 © SEMI 2000 2 6.2.2.2.2 The m arkers made on the spec i m en stage should show the X- an d Y-direct ion of s pecimen-stag e movement, and th e a ngle between the tw o markers should be 90° ± 0.1° (See Fi gu…

SEMI P36-0600 © SEMI 20001

SEMI P36-0600

GUIDELINE OF MAGNIFICATION REFERENCE FOR CRITICAL

DIMENSION MEASUREMENT SCANNING ELECTRON MICROSCOPES

(CD-SEMS)

This guideline was technically approved by the Global Metrology Committee and is the direct responsibility

of the Japanese Metrology Committee. Current edition approved by the Japanese Regional Standards

Committee on March 1, 2000. Initially available at www.semi.org May 2000; to be published June 2000.

1 Purpose

1.1 The purpose of this guideline is (1) to define

common and important specifications of magnification

references which are used for calibrating magnifications

of critical dimension measurement scanning electron

microscopes (CD-SEMs), and as the result (2) to

provide magnification references which are easy for

anyone to use.

2 Scope

2.1 It is preferable that design, manufacture and

purchase specifications for CD-SEM magnification

references conform to this guideline.

2.2 This standard does not purport to address safety

issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory limitations prior to use.

3 Referenced Standards

3.1 None.

4 Terminology

4.1 CD-SEM magnification refere nce



a CD-SEM

magnification reference is defined as a standard for

calibrating magnifications of a said CD-SEM through

mounting the standard on the specimen stage,

measuring the dimensions of reference patterns formed

on the standard, determining the difference between the

measurement value and the true or reference value of

the reference patterns, and adjusting the CD-SEM

parameters to bring the difference zero.

4.1.1 There are two types of CD-SEM magnification

references: one is a wafer on which reference patterns

are formed; another is a chip on which reference

patterns are formed. Hereinafter, the former will be

referred to as “wafer-type magnification reference,” and

the latter will be referred to as “chip-type magnification

reference.”

4.2 edge roughness  Edge rough ness refers to edge

variations seen in the SEM images, and is defined as

the distance, within a field of view, between the peak

line and the valley line, where the peak line means the

line which runs through the highest peak and is parallel

to the pattern-edge mean line, the valley line means the

line which runs through the lowest valley and is parallel

to the pattern-edge mean line, and the pattern-edge

mean line conforms to the expected pattern-edge line.

Here, a peak is the tip of a convex section, and a valley

is the deepest part of a concave section (See Figure 1).

5 Ordering Information

5.1 Specify whether a said CD-SEM magnification

reference is a wafer-type magnification reference or a

chip-type magnification reference.

6 Requirements

6.1 CD-SEM Magnification References and Their

Structure

6.1.1 CD-SEM Magnification References are either

wafer type or chip type. Chip types are composed of a

chip (or chips) and a stub to hold the chip (or chips).

Wafer type include a 'drop-in' wafer which is a wafer

with a thinned section where a die with the reference

calibration pattern can be dropped in.

6.2 Shape, Size and Mounting Method of CD-SEM

Magnification References

6.2.1 Shape and size of wafer-type magnification

references, and method of mounting them on the

specimen stages in CD-SEMs must follow the shape,

size and mounting method of product wafers.

6.2.2 Shape and size of chip-type magnification

references, and method of mounting them on the

specimen stages of CD-SEMs are defined as follows:

6.2.2.1 Size and shape of chip-type magnification

references: See Figure 2.

6.2.2.2 Mounting method of chip-type magnification

references:

6.2.2.2.1 A magnification reference should be

mounted on a specimen stage as markers made on the

stub fit in markers made on the specimen stage, and be

fixed by using a screw. The markers made on the stub

should show the direction of reference patterns at an

accuracy of within ± 1°.

SEMI P36-0600 © SEMI 2000 2

6.2.2.2.2 The markers made on the specimen stage

should show the X- and Y-direction of specimen-stage

movement, and the angle between the two markers

should be 90° ± 0.1° (See Figures 2 and 3).

6.2.2.3 Chip surface height for chip-type

magnification references:

6.2.2.3.1 The height of chip surface (or reference

pattern surface) from the specimen stage surface should

be 1.7 ± 0.05 mm as the magnification reference is

mounted on the specimen stage.

6.3 Materials for Magnification R eferences



Materials for magnification references must be non-

magnetic and conductive.

6.3.1 Wafers for wafer-type magnifi cation references

and chips for chip-type magnification references are

preferable to be silicon.

6.3.2 Materials of the stub for chip-t ype magnification

references are preferable to be aluminum, copper, or

carbon.

6.4 Properties of Magnification Reference Pattern

6.4.1 Reference patterns do not change or degrade in

use.

6.4.2 The block area of reference patterns (or every

block area, in the case where there are some reference

pattern blocks) must be larger than 100 µm × 100 µm,

and the block should be placed so that it is easily

recognizable.

6.4.3 The pattern-edge roughness must be within the

calibration uncertainty described in Section 6.5.5.

6.5 Report

6.5.1 Suppliers of CD-SEM magnification references

must report the following to the purchaser.

6.5.2 Wafer material for wafer-type magnification

references, or chip and stub materials for chip-type

magnification references: e.g., silicon chip, aluminum

stub, etc.

6.5.3 Type of reference patterns: e.g., dense lines, etc.

6.5.4 Figures and/or pictures of the reference patterns

with pattern dimensions which show top and/or cross

sectional view.

6.5.5 Calibration uncertainty of reference patterns:

e.g., line pitch 180

± 1 nm at 95% confidence level, etc.

6.5.6 Traceability and its certification organization,

and measurement method used for deciding the

calibration uncertainty of reference patterns: e.g., the

uncertainty was decided in terms of mean value and

variation obtained by means of a precise diffraction

angle measurement using a He-Cd laser beam of a 2

mm spot diameter, and was certified by NMI (National

Metrology Institute), etc.

NOTE 1: Traceability is the property of the calibration of the

reference patterns whereby it can be related to stated

references, usually national or international standards, through

an unbroken chain of comparison of all having stated

uncertainties. Refer to the international vocabulary of basic

and general items in metrology, ISO, 1993, 60 p., ISEN 92-67

01075-1.

6.5.7 Applicable magnification range: e.g., 50k×–

200k×, etc.

6.5.8 Notices of caution for cleaning and maintenance:

e.g., whether cleaning is possible or not, and if possible,

the process of cleaning, procedures for storage, etc.

center-to-center pitch

centerline

pattern edge mean line

least squares best fit line

linewidth

peak-to-peak edge

roughness

defined measurement length

segment

linewidth

peak line

valley line

peak

valley

NOTE 1: The figure ignores that fact that the SEM image is gray-scale and not black and white. Use the same intensity threshold

setting for measuring pitch as for line width The center-to-center pitch averaged over the measurement length segment is to be

certified and used for SEM magnification calibration

Figure 1

Definition of Edge Roughness

chip

stub

chip surface*

φ15

≈10.5

1.7±0.05

−0.032

−0.050

marker

stub

≈

* The flatness of the chip

surface to the specimen stage

surface could be automatically

determined by setting the

magnification reference on the

specimen stage.

Figure 2

Shape and size of chip-type magnification reference: unit mm