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SEMI M53-1103 © SEMI 2003 8 APPENDIX 1 SINGLE-POINT CALIBRATION NOTICE : The ma terial in this ap pendix is an official part of SEMI M 53 and was a pproved by full lette r ballot procedures on No vember 22, 200 2. A1-1.1…

SEMI M53-1103 © SEMI 2003 7

11.1.2 Date and location of measurement;

11.1.3 Manufacturer, model, serial number, and

software version of the SSIS;

11.1.4 Reference wafer characteristics as outlined in

the certificates accompanying the reference wafers (See

Section 8.4);

11.1.5 Histogram for each data set and the assigned

peak value of the distribution of reported diameters

together with the certified peak diameter of the PSL

sphere distributions used to generate the histogram; and

11.1.6 The curve fitted to the peak values and the

associated certified PSL diameters.

SEMI M53-1103 © SEMI 2003 8

APPENDIX 1

SINGLE-POINT CALIBRATION

NOTICE: The material in this appendix is an official part of SEMI M53 and was approved by full letter ballot

procedures on November 22, 2002.

A1-1.1 Choose a single reference wafer with PSL

sphere deposition CRM size near the LSE size of the

smallest LLS to be tested for in meeting a wafer

specification.

NOTE A1-1: Because of possible non-linearities in the SSIS,

single-point calibration is not recommended except in the

immediate vicinity of a single sphere size of interest, for

example, the smallest size to be tested for in meeting a wafer

specification.

A1-1.2 Set up the SSIS to be calibrated in accordance

with Sections 9.1 and 9.2.

A1-1.3 Load the appropriate reference wafer into the

SSIS.

A1-1.4 Scan the wafer.

A1-1.5 Generate a data set file of the distribution of

localized light scatterers as a function of reported size

(LSE).

A1-1.6 Construct a histogram for the distribution in the

data set file.

A1-1.7 Determine the standard deviation and peak

diameter value from curve fits of the histogram.

A1-1.8 Associate the peak value of reported size (LSE)

found to the certified value of PSL sphere diameter

deposited on the reference wafer.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer's instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

By publication of this standard, Semiconductor

Equipment and Materials International (SEMI) takes no

position respecting the validity of any patent rights or

copyrights asserted in connection with any items

mentioned in this standard. Users of this standard are

expressly advised that determination of any such patent

rights or copyrights, and the risk of infringement of

such rights are entirely their own responsibility.

SEMI M53-1103 © SEMI 2003 9

RELATED INFORMATION 1

DEPOSITION ISSUES

NOTICE: This related information is not an official part of SEMI M53 and was derived from the work of the

Automated Wafer Surface Inspection Task Force. This related information was approved for publication by full

letter ballot on November 22, 2002.

R1-1.1 Both this practice and SEMI M52 introduce the

notion that SSIS calibration should depend on the

characteristics of PSL sphere depositions as they appear

on the reference wafers, rather than the previous

technique of using the bulk characteristics of the PSL

spheres measured prior to being deposited. This change

in philosophy has come about for two reasons. First, in

many situations, there is actually some advantage to

creating depositions with different characteristics from

those of the bulk PSL spheres. For example, the

deposition process may be used to narrow the diameter

distribution thus creating a standard that more closely

approximates a source of particles of a single known

size. Secondly, most deposition systems produce at

least minor changes in diameter distributions that are

difficult to eliminate in any case. As a result, this

philosophical change is being introduced to increase the

accuracy with which SSIS calibration can be

accomplished.

R1-1.2 Deposition systems generally consist of an

atomizer (which takes the particles from a liquid

suspension to an air droplet mist), followed by a dryer

(so that droplets of the source liquid do not reach the

wafer), and often include a bipolar charger and

differential mobility analyzer (or DMA) to size and/or

filter the particles. The changes in characteristics from

source to deposition are due to at least three distinct

causes. First, virtually all atomizers bias the diameter

distribution slightly in favor of smaller particles. This

is because the larger particles do not “fit” in the smaller

droplets and as a result have a smaller probability of

ending up in the airborne stream of particles headed

towards the wafer. For narrow source distributions this

is not much of an issue, but for wider source

distributions it is. Secondly, the source liquid often

contains non-volatile solids that may dry onto the

particles, thus slightly changing their diameter.

Although this is not as important for larger particles

greater than 200 nm, it is highly recommended that a

PSL suspension with low non-volatiles be used to

reduce this source of error. If the DMA is operated in a

manner that meets the requirement of this practice for

distributions with full width at half maximum (FWHM)

of no more than 5% of the peak diameter, then many

source distributions are narrowed by the DMA. This is

true because many PSL sphere sources with diameters

less than 200 nm have FWHM values wider than 5% of

peak value. The 5% FWHM value does not impose

severe difficulties on the DMA design.

R1-1.3 In addition to narrowing the deposition

diameter distributions, these standards address related

accuracy issues. These are easily understood by

considering the filtering process of the DMA on the

source distribution as shown in Figure R1-1. The left

hand side of the figure represents a rather broad PSL

source diameter distribution. Notice that it is not

symmetrical, which makes the mean (or average)

diameter different from the modal (or peak) diameter.

Typically PSL manufacturers have given the mean

diameter with their product and industry users have

assigned this value as the diameter for that deposition.

Unfortunately depositions are generally made at the

peak diameter. This is because the peak is easily found

by scanning the DMA through the source distribution

while counting the number of particles passing the

DMA. The center section of the figure shows the ideal

triangular transfer function of the DMA fixed at some

center diameter. By adjusting airflows through the

DMA, the FWHM can be changed. By adjusting an

applied voltage, the center pass diameter of the transfer

function can be changed. In effect, the deposition

characteristics are formed through the multiplication of

the transfer function with the source distribution as

indicated on the right hand side of the figure.

R1-1.4 Notice that the shape of the deposition

distribution is triangular with bowed in sides, because

the source distribution is not flat. In effect, this is a

safety factor for the 5% FWHM specification. Because

the source distribution is not necessarily symmetrical,

the deposition distribution may not be either; however,

the mean and peak deposition diameters will be very

close because the distribution is relatively narrow.