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SEMI M42-1000 © SE MI 2000 2 5 Wafer Ord ering Inf ormat io n 5.1 Purch ase orders for epitaxial la y e r s must include the following items: 5.1.1 T he s ubstrate (as descri bed by t he relevant SEMI Standard). 5.1.2 Th…

SEMI M42-1000 © SEMI 20001

SEMI M42-1000

SPECIFICATION FOR COMPOUND SEMICONDUCTOR EPITAXIAL

WAFERS

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

direct responsibility of the North American Compound Semiconductor Committee. Current edition approved

by the North American Regional Standards Committee on August 28, 2000. Initially available at

www.semi.org September 2000; to be published October 2000.

1 Purpose

1.1 Compound semiconductor epitaxial layers have

been extensively used for many years as the basis of

high speed electronics and optoelectronic devices.

There are suppliers of epitaxial layers who will grow

material to the customer’s specification. There is a

need to define standardized descriptive terms, tolerance

schedules and recommended test methods to reduce

ambiguity in the interpretation of specifications for

such wafers. Special emphasis is placed on the

definitions pertaining to uniformity. This proposed

document addresses only the basic requirements.

Further clarification may be required between supplier

and purchaser for the particular layers required.

2 Scope

2.1 These specifications cover the requirements for

epitaxial layers of the generic composition A

...N

grown on monocrystalline wafers of GaAs or InP (other

substrates may be considered where appropriate

documents exist to describe the specification of the

substrate). This document may only cover a portion of

the properties considered to be part of the purchase

specification.

2.2 This specification does not purport to address

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

responsibility of the users of this specification to

establish appropriate safety and health practices and

determine the applicability of regulatory limitations

prior to use.

3 Referenced Standards

3.1 SEMI Standard

SEMI M1 — Specifications for Polished

Monocrystalline Silicon Wafers

3.2 ASTM Test Methods

ASTM F76  Standard Test Methods for Measuring

Resistivity and Hall Coefficient and Determining Hall

Mobility in Single-Crystal Semiconductors.

1 American Society for Testing and Materials, 100 Barr Harbor

Drive, West Conshohocken, PA 19428-2959

ASTM F673  Standard Test Methods for Measuring

Resistivity of Semiconductor Slices or Sheet Resistance

of Semiconductor Films with a Noncontact Eddy

Current Gage.

3.3 DIN Standard

DIN 50447 — Contactless Determination of the

Electrical Sheet Resistance of Semiconductor Layers

with the Eddy Current Method

4 Terminology

4.1 epitaxy — the growth of a single crystal layer on a

substrate of the same material, homoepitaxy; or on a

substrate of different material with compatible crystal

structure, heteroepitaxy

4.2 fixed quality area (FQA) — (refer to Figure 1 of

SEMI M1) the central area of the wafer surface, defined

by a nominal edge exclusion, X, over which the

specified values of a parameter apply.

4.3 mismatch — the ratio, m

, defined by the lattice

constant of the epitaxial layer perpendicular to the

surface, c, minus that of the substrate, a

divided by the

substrate lattice constant.

= (c – a

)/a

4.4 mole fraction — the normalized fraction of a

particular element occupying the same lattice site in a

compound. E.g. in the compound A

, a, b, c and

d are the mole fractions of the elements A, B, C and D

respectively. If, in this example, A and B share the

same lattice site, and C and D share the other lattice

site, then by definition the sum of a and b, and the sum

of c and d each must be 1.

4.5 graded layer — a layer whose properties vary

smoothly in the direction perpendicular to the surface.

The properties of a graded layer are specified in terms

of the parameters at the top (last to grow surface) and

bottom (first to grow surface) of the layer and unless

otherwise specified, are expected to vary linearly

between these two end values.

2 Deutsches Institut für Normung e.V., available from Beuth Verlag

GmbH, Burggrafenstrasse 4-10, D-10787 Berlin, Germany

SEMI M42-1000 © SEMI 2000 2

5 Wafer Ordering Informatio n

5.1 Purchase orders for epitaxial layers must include

the following items:

5.1.1 The substrate (as described by the relevant SEMI

Standard).

5.1.2 The epitaxy growth method.

5.1.3 The nominal edge exclusion used to define the

FQA.

5.1.4 The composition of each layer in terms of mole

fraction(s) and a description of the test method used to

measure it and/or calibrate the growth conditions of that

layer. Note that in the case of a ternary compound, the

purchaser may require that the specification for

mismatch or bandgap energy take precedence over that

for nominal composition. Similarly in the case of a

quaternary compound, a specification of mismatch and

bandgap energy may be preferred. This is because the

mismatch and bandgap energy, which depend on the

composition, are often easier to measure than the

composition directly.

5.1.5 The thickness of each layer and a description of

the test method used to measure it and/or calibrate the

growth conditions of that layer.

5.1.6 The dopant used for each layer.

5.1.7 The carrier concentration of each layer and a

description of the test method used to measure it and/or

calibrate the growth conditions of that layer. In the

case of layers with significant interface or surface

depletion, the carrier concentration refers to the value

that would be observed in thicker layers, once the

appropriate correction is applied for interface and

surface depletion effects.

5.1.8 Optional Criteria — The follo wing items may

also be specified in addition to those listed above.

5.1.8.1 The mobility of each layer.

5.1.8.2 The sheet resistance of the epitaxial layers.

5.1.8.3 The mismatch for each layer. The test method

must be described.

5.1.8.4 The bandgap energy for each layer. The test

method must be described.

5.1.8.5 The sheet carrier concentration and mobility of

the whole structure. This is relevant to those structures

where the carriers are expected to redistribute to an

adjacent material or interface.

5.1.8.6 The surface defect density.

5.1.8.7 The end values and thickness of each graded

layer.

5.1.8.8 The surface roughness. The test method must

be described.

5.1.8.9 The growth and test methods of a calibration

structure along with a schedule for the growth of such a

structure.

6 Tolerance Requirements

6.1 The tolerance requirements for the specified

parameter, unless otherwise agreed to between the

supplier and purchaser, are as in Table 1. Tolerance is

defined as the allowed range of values permissible

within the FQA and includes variations due to non-

uniformity and deviation from the customer’s target

value. The measurement point schedule (map of

measurement points) should be agreed upon between

the supplier and purchaser. Three classifications are

given for products of varying control needs.

Table 1 Parameter and Tolerance Requirements

Parameter Tolerance A Tolerance B Tolerance C

composition

[mole fraction (s)] ± 0.05 ± 0.01 ± 0.005

thickness

[percent of nominal] ± 20% ± 10% ± 5%

carrier concentration

[percent of nominal] ± 20% ± 10% ± 5%

sheet resistance

[percent of nominal] ± 20% ± 10% ± 5%

Table 2 Parameter and Recommended Measurement Technique

Parameter Technique Test Method

composition infer from bandgap energy measured by

photoluminescence, or photo reflectance

and/or from mismatch measured by high resolution X-ray

diffractometry

under development

none as yet

thickness cleaved cross sections measured by optical or scanning

electron microscopy

and/or profilometry of selectively etched layers

needs revision

none as yet

carrier concentration Hall effect

or C-V profiling (electrochemical or mercury probe)

ASTM F 76- needs revision

none as yet

sheet resistance Van der Pauw technique

and/or eddy current

ASTM F 76

ASTM F 673 or DIN 50447

mobility Hall effect ASTM F 76

7 Test Methods

7.1 Measurements shall be carried out according to the

methods outlined in Table 2. Where no methods are

specified, or where choices are given, the supplier and

purchaser shall agree in advance on the means for

making the measurement.

7.2 Given the state of development for the

recommended test methods and the lack of standard

reference materials, it is advisable that the vendor and

purchaser exchange samples to cross calibrate their

measurement instruments and procedures.

8 Marking

8.1 In addition to the requirements set out in the

specification for the substrates, a unique number

traceable to the growth run shall be identified on the

supplier’s certificate.

9 Certification

9.1 Upon request of the purchaser in the contract or

order, a manufacturer’s or supplier’s certification that

the material was manufactured and tested in accordance

with this specification, together with a report of the test

results, shall be furnished at the time of shipment.

9.2 The user and supplier may agree that the material

shall be certified as “capable of meeting” certain

requirements. In this context, “capable of meeting”

shall signify that the supplier is not required to perform

the appropriate tests in Section 7; however, if the user

performs the test and the material fails to meet the

requirement, the material may be subject to rejection.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standard 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 mentioned herein. These

standards are subject to change without notice.

The user’s attention is called to the possibility that

compliance with this standard may require use of

copyrighted material or of an invention covered by

patent rights. By publication of this standard, SEMI

takes no position respecting the validity of any patent

rights or copyrights asserted in connection with any

item 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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the contents in whole or in part is forbidden without express written

consent of SEMI.