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SEMI MF1618-1104 © SEMI 2004 5 9.3.2 Standard Devi ation Uniformity, SUP , in percent: 100 (%)   x s SUP (4) 10 Report 10.1 Repo rt the fol lowing informat ion when describin g the uniformity of a specific thin film pa…

SEMI MF1618-1104 © SEMI 2004 4

6 Summary of Practice

6.1 Measurements are made at the sites specified in the

chosen sampling plan using the appropriate

instrumentation and measurement procedure for the

film parameter of interest. Measures of the dispersion

of the values are obtained by simple statistics specified

for the sampling plans.

7 Apparatus

7.1 Four-probe Sheet Resistance, Eddy-current,

Mercury Probe CV, Spectroscopic Reflectometers,

Ellipsometers, Interferometers, and Stylus

Profilometers — Typical apparatus chosen according to

the type of material parameter being monitored. Others

may be chosen according to need. The instrumentation

should include such features as temperature monitoring

and control, EMI shielding, shielding from

illumination, etc. as is necessary for good practice of

that type of measurement. In addition, all

instrumentation must include the following:

7.1.1 Ability to center the wafer on the measurement

stage to an accuracy of 0.5 mm or better,

7.1.2 Vacuum chuck, or similar fixture, to secure the

wafer to the instrument stage during measurement,

7.1.3 Ability to locate the measurement points

specified in the chosen sampling plan to an accuracy of

0.5 mm or better, and

7.1.4 Ability to store all measurement data to perform

the required calculation of uniformity.

7.2 Capability of the instrumentation to perform one or

more of the following auxiliary data presentations is

highly recommended:

7.2.1 Generating a two-dimensional contour map of the

acquired data,

7.2.2 Generating a histogram of the raw data values,

and

7.2.3 Presenting the raw data as a time-series plot.

7.3 Capability to edit data and to blend or interpolate

data in conjunction with two-dimensional mapping may

be useful, but it should be done with caution.

8 Procedure

8.1 Calibrate the measurement system in accordance

with the manufacturer’s instructions or with the

applicable test method.

8.2 Place the wafer on the instrument stage so as to

locate the wafer center within 0.5 mm of the center of

the stage. For the purposes of this procedure, the wafer

center is considered to be defined by the intersection of

any two diameters that do not intersect a wafer flat or

orientation notch.

8.3 Select the sampling plan to be used from those

listed in Appendix 1 and proceed to take measurements

at all the specified locations. It may be necessary to

enter the coordinates of the desired sampling plan into

instrument software, or to work with the manufacturer

of the equipment to modify its software if the sampling

plans available in the instrument do not match the

requirements of Appendix 1.

8.4 Take measurements at all locations specified for

the selected sampling plan. Then quantify the

uniformity from the acquired data using the calculations

specified in Section 9.

9 Calculations

9.1

Calculate the mean,

x , and the standard deviation,

s, of the N measurement values, x

, as follows:





, and (1)

2/1

)(





















s (2)

9.2 Examine the data. If agreed upon between parties

to the test, reject values that are away from the mean by

more than three times the standard deviation calculated

in Section 9.1. Recalculate the mean and standard

deviation using Equations 1 and 2, where N is now the

reduced number of data points.

NOTE 1: It is generally advisable, through use of a time

series plot of the original data, or similar means, to inspect the

data just rejected for determination of measurement site

location and relation to adjacent measurement values.

NOTE 2: The calculation for standard deviation may be

made regardless of any systematic behavior of the underlying

distribution of measured values. However, when there is a

systematic spatial behavior to the measured values, the

standard deviation may not be used to estimate confidence

intervals or tolerance limits.

9.3 Calculate the following two statistics from the

complete data set or from the reduced data set if certain

measurements were rejected in Section 9.2. These two

statistics represent the range and the distribution of data

about the mean. The use of only one of these statistics

is at the discretion of the interested parties.

9.3.1 High-Low Variation, HLV, in percent:

200(%)

minmax









HLV

(3)

SEMI MF1618-1104 © SEMI 2004 5

9.3.2 Standard Deviation Uniformity, SUP, in percent:

100(%) 

SUP (4)

10 Report

10.1 Report the following information when describing

the uniformity of a specific thin film parameter across

the surface of a wafer:

10.1.1

Wafer identification and diameter,

10.1.2 Operator and date,

10.1.3 Substrate type (orientation and doping, if

appropriate),

10.1.4 Generic film type, and reactor, run or process

information, as appropriate,

10.1.5

Film parameter measured and assumed material

constants used for analysis,

10.1.6 Sampling plan used,

10.1.7 Test method used by designation, if available, or

by brief description if no standard procedure is

available,

10.1.8

Test instrument manufacturer, model, options,

10.1.9 Total number of points measured; number of

points within 3-sigma; number of points used to

calculate HLV and SUP,

10.1.10 Calculated HLV(%), SUP(%), mean value (

x ),

and sample standard deviation, s.

10.2

Two-dimensional contour plot, data histogram, or

time series plot of measurement values may be included

if agreed upon between the parties to the test.

10.3 For a single-diameter sampling plan, also report

the angle between the diameter measured and the

fiducial axis.

11 Precision and Bias

11.1 Precision — The precision with which wafer

uniformity can be measured is governed by the

precision of the individual test method being used.

11.2

Bias — The bias associated with the wafer

uniformity measurements is also governed by the bias

of the individual test method being used.

11.3

The Precision and Bias sections of the test method

being used should be consulted.

NOTE 3: The Appendix

of SEMI MF81 gives, for the case

of sparse site sampling plans, an example of the propagation

of error from the basic measurement technique to the

determination of variation of material properties using that

technique.

11.4 The standard deviation and range calculations that

are specified in Section 9 are descriptive statistics or

figures of merit for describing the uniformity of the thin

film wafer in a simple and consistent manner, but they

are generally not appropriate for determining the

precision of the measurements.

12 Keywords

12.1 dielectric layers; epitaxial layers; ion implant;

metal films; sampling plans; semiconductor; silicon;

thin films; uniformity

1 This non-mandatory section will be called Related Information after

this standard has been reformatted and adopted through the SEMI

Standards process.

SEMI MF1618-1104 © SEMI 2004 6

APPENDIX 1

SAMPLING PLANS TO BE USED FOR WAFER UNIFORMITY

DETERMINATION

NOTICE: The material in this appendix is an official part of SEMI MF1618 and was approved by full letter ballot

procedures.

A1-1 Introduction

A1-1.1 For all plans, measurements are made within a

circular area defined by the radius, R

, between the

center of the wafer and the circle on which the centers

of the outermost measurement sites lie. Determine this

radius by either of the following methods:

A1-1.1.1

Method A — In this method, the outermost

edges of the measurement spots on the outermost radius

are tangent to the boundary of the fixed quality area

(FQA) as defined in SEMI M1:

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









 )

(

(A1-1)

where:

= radius of the outermost measurement circle (see

Figure A1-1),

D = nominal diameter of the wafer, for example,

100, 150, 200, or 300 mm,

EE = nominal wafer edge exclusion, which

determines the FQA, and

d = known or estimated diameter of the

measurement spot for the test instrument being

used (Note 1).

NOTE 1: The exact diameter of the measurement spot may

not be known for many types of measurements. Estimate the

diameter as 1.5 times the probe spacing for a four-point probe,

transducer radius for an eddy-current instrument, and apparent

beam spot radius for optical measurements if no other

information is available.

A1-1.1.2 Method B — In this method, the centers of the

measurement spots on the outermost radius are on the

boundary of the fixed quality area (FQA) as defined in

SEMI M1:

















(A1-2)

where the symbols are defined following Equation A1-

A1-2 Selection of Method

A1-2.1 Neither of these methods is “better” than the

other; rather, there are tradeoffs.

A1-2.2

The location of every point in a multipoint

measurement pattern depends on the method chosen to

define the position of the outermost measurement sites.

Therefore, there may be differences between the two

methods for reported individual and statistical values.

A1-2.3

Data for a measurement site are usually reported

at the location corresponding with the center of the

measurement spot.

A1-2.4

Data from each measurement on the outermost

ring in Method A are not affected by the film properties

in the edge exclusion annulus outside the FQA.

However, in this case, data are not reported for

locations closer to the boundary of the FQA than the

measurement spot radius.

A1-2.5

Conversely, data from each measurement on the

outermost ring with Method B include contributions

from film properties both inside and outside the FQA.

In this case, measurement data is reported for locations

up to the boundary of the FQA, but establishing the

significance of including data influenced by film

properties outside the FQA is outside the scope of this

practice.

NOTE 2: Measurements obtained using a probe whose

effective measurement area extends beyond the edge of the

film inaccurately represent actual film properties.

Figure A1-1

FQA Boundary and Outermost Ring Radii, R

, for

Methods A and B