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SEMI M53-1103 © SEMI 2003 10 R1-1.5 The accuracy of the peak diameter, which is specified to have a relative exp anded uncertainty at about 95% confidence level as small as possible but not greater than 3% in SEMI M52, i…

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.

SEMI M53-1103 © SEMI 2003 10

R1-1.5 The accuracy of the peak diameter, which is specified to have a relative expanded uncertainty at about 95%

confidence level as small as possible but not greater than 3% in SEMI M52, is determined by either the accuracy

with which the peak source diameter is known (or can be found), or by the accuracy of the DMA sweep

voltage/diameter relationship. Unfortunately many PSL source bottles currently in use do not give the peak

diameter, so this presents a difficulty for the first approach. The second approach, relying on DMA voltage

accuracy, can be checked by using PSL sources that are known to be very narrow (to minimize differences between

source and deposition peak diameter) with very accurate peak values.

PSL Source Diameter

Distribution

Mean, or

average,

diameter

Peak, or

modal,

diamete

Diameter

Counts/Diameter

X =

Deposition Transfer

Function

In many deposition

systems, the transfer

function may be scanned

through the diameter

distribution and set to the

eak diameter.

Transmission

Diameter

Deposition Diameter

Distribution

Diameter

Counts/Diameter

The shape of the

deposition diameter

distribution is no

wider than the

transfer function.

Figure R1-1

The Diameter Distribution of the Deposition is the Product of the Deposition System Transfer Function and

the Source (or “Bottle”) Distribution.

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.

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consent of SEMI.

SEMI M54-0304 © SEMI 2003, 2004 1

SEMI M54-0304

GUIDE FOR SEMI-INSULATING (SI) GaAs MATERIAL PARAMETERS

This guide was technically approved by the Global Compound Semiconductor Committee and is the direct

responsibility of the European Compound Semiconductor Materials Committee. Current edition approved by

the European Regional Standards Committee on January 9, 2004. Initially available at www.semi.org

February 2004; to be published March 2004. Originally published March 2003.

1 Purpose

1.1 Substrates with high electrical resistivity and

electron drift mobility are needed to fabricate high

performance digital and analog microelectronic devices

and circuits. Semi-insulating n-type Gallium Arsenide,

henceforth termed SI GaAs, has been established

worldwide as a preferred substrate material for such

applications.

1.2 The active layers needed for devices are generated

either by ion implantation or by epitaxy. The quality of

these layers, and hence the performance, yield and

reliability of devices, strongly depends on the bulk and

surface quality of the substrate.

1.3 This document provides a basis for specifying the

material parameters of SI GaAs to support ordering

agreements between suppliers and purchasers.

2 Scope

2.1 This document defines and describes the electrical,

optical, structural, and surface properties of SI GaAs

that are considered technically relevant according to the

present status of scientific knowledge and material

technology.

2.2 A specification of the material quality of SI GaAs

substrates includes a number of the parameters

described below. Depending on the intended

application, a particular subset of properties and

respective parameters will be considered relevant by the

purchaser.

2.3 In order to enhance the clarity and applicability of

the document, the ordering information in Section 6

subdivides the material parameters in respect of their

relative importance, according to general industry

perception.

2.4 Some material properties and parameters, while

intensively discussed in the technical literature, are

insufficiently established to allow an unambiguous

specification. The available information is nevertheless

included to support supplier-purchaser discussions and

agreements on these issues.

2.5 Each parameter specification requires an agreement

about verification. Appropriate information is

summarized in Section 5. Available standard test

methods elaborated by SEMI, ASTM, and DIN are

referenced in Section 3.

2.6 A number of the required standard test methods do

not exist at present. This document is expected to serve

as a guideline and incentive for qualified ASTM, DIN,

JEITA, and SEMI committees to develop the missing

standard procedures. Conversely, if at present more

than one standard test method for verification of a

specific parameter exists (see Table 1), a global

consensus procedure towards selecting or generating a

unique standard is advocated.

2.7 The geometrical properties of wafers, in particular

orientation, diameter, thickness, flatness and edge

rounding, are covered by the series of SEMI M9

specifications and shall not be addressed here.

NOTICE: 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 or other limitations prior

to use.

3 Referenced Standards

3.1 SEMI Standards

SEMI M9 — Specifications for Polished

Monocrystalline Gallium Arsenide Slices

SEMI M10 — Standard Nomenclature for

Identification of Structures and Features Seen on

Gallium Arsenide

SEMI M15 — Polished Wafer Defect Limits Table for

Polished Gallium Arsenide Wafers

SEMI M30 — Standard Test Method for Substitutional

Atomic Carbon Concentration in GaAs by Fourier

Transform Infrared Absorption

SEMI M36 — Test Method for Measuring Etch Pit

Density (EPD) in Low Dislocation Density Gallium

Arsenide Wafers

SEMI M39 — Test Method for Measuring Resistivity

and Hall Coefficient and Determining Hall Mobility in

Semi-insulating GaAs Single Crystals