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SEMI MF1239-0305 © SEMI 2003, 2005 2 NOTICE : This standard does not purport to address saf ety issu es, if any, associated with its use. It is the responsibility of the user of this stan dard to establish appropriate sa…
SEMI MF1239-0305 © SEMI 2003, 2005 1
SEMI MF1239-0305
TEST METHOD FOR OXYGEN PRECIPITATION CHARACTERISTICS
OF SILICON WAFERS BY MEASUREMENT OF INTERSTITIAL OXYGEN
REDUCTION
These test methods were technically approved by the Global Silicon Wafer Committee and are the direct
responsibility of the North American Silicon Wafer Committee. Current edition approved for publication by
the North American Regional Standards Committee on December 10, 2004. Initially available at
www.semi.org January 2005; to be published March 2005. Original edition published by ASTM
International as ASTM F 1239-89. Last previous edition SEMI MF1239-02.
1 Purpose
1.1 Oxide precipitates in the bulk of a silicon wafer can act as gettering sites for contamination that may be
introduced during manufacture of circuits and devices. This contamination (usually metallic impurities), if not
gettered, can reduce device manufacturing yields and degrade device or circuit performance. Thus, the oxygen
precipitation characteristics of the silicon wafer can significantly affect both yields and performance.
1.2 Although interstitial oxygen concentration is an important factor in affecting the amount of oxygen precipitation
that occurs in silicon during a specific thermal cycle, the presence of other impurities such as carbon or nitrogen, and
differences in dopant type and density, thermal history, or defect properties of the crystal can also affect the
precipitation characteristics. Thus, it is frequently necessary to choose particular material properties and preparation
techniques to obtain the desired precipitation characteristics for a particular application.
1.3 This test method may be used to compare the oxygen reduction of two or more groups of silicon wafers. This
test method is based on thermal cycles that simulate certain common device processing cycles.
1.3.1 Cycle A, a one-step precipitation cycle, provides an indication of the native nucleation sites present in the as-
received wafers.
1.3.2 Cycle B, a two-step nucleation-precipitation cycle, simulates the precipitation that occurs in normal n-MOS
device processing.
1.4 These test methods may be used to compare qualitatively the precipitation characteristics of two or more groups
of wafers.
1.5 These test methods may also be used to determine the uniformity of oxygen reduction across a wafer (in
conjunction with SEMI MF951) or from wafer to wafer within a lot.
2 Scope
2.1 These test methods cover complementary procedures for testing the oxygen precipitation characteristics of
silicon wafers. It is assumed that the precipitation characteristics are related to the amount of interstitial oxygen lost
during specified thermal cycles.
2.2 These test methods may be applied to any n- or p-type Czochralski silicon wafers of any orientation whose
thickness, resistivity, and surface finish are such as to permit the oxygen concentration to be determined by infrared
absorption and whose oxygen concentration is such as to produce measurable oxygen loss.
2.3 These test methods are not suitable for determining the width or characteristics of a “denuded zone,'' a region
near the surface of a wafer that is essentially free of oxide precipitates.
2.4 Because these test methods are destructive, suitable sampling techniques must be employed.
2.5 Determination of material performance in actual device fabrication situations is beyond the scope of these
methods. However, by comparing the results of these tests with actual device yields and performance, criteria for
selection of specific material characteristics may be established.
2.6 The values stated in SI units are regarded as standard.
SEMI MF1239-0305 © SEMI 2003, 2005 2
NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and health guides and determine the
applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 All factors that affect the infrared absorption measurement (including differences in back surface condition,
instrumental characteristics, and wafer resistivity) may cause errors in the determination of oxygen reduction.
3.2 If significant quantities of oxygen are outdiffused during the thermal cycles, the measured oxygen reduction
may not be representative of the amount of oxygen precipitation.
3.3 If precipitate size varies from sample to sample, the variations in measured oxygen reduction may not be
representative of variations in the number of oxide precipitates that are formed.
3.4 The specified thermal cycles may or may not provide adequate simulation of the cycles used in a particular
device processing sequence. The results obtained in these test methods can serve as predictors of those expected in
actual device processing only to the extent that the simulation is representative of the device process.
4 Referenced Standards
4.1 SEMI Standards
SEMI C28 — Specifications and Guidelines for Hydrofluoric Acid
SEMI C29 — Specifications and Guideline for 4.9% Hydrofluoric Acid 10:1 v/v
SEMI C54 — Specifications and Guidelines for Oxygen
SEMI C59 — Specifications and Guidelines for Nitrogen
SEMI M59 — Terminology for Silicon Technology
SEMI MF951 — Test Method for Determination of Radial Interstitial Oxygen Variation Silicon Wafers
SEMI MF1188 — Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption with Short
Baseline
SEMI MF1619 — Test Method for Measurement of Interstitial Oxygen Content of Silicon Wafers by Infrared
Absorption Spectroscopy with p-Polarized Radiation Incident at the Brewster Angle
4.2 ASTM Standard
D 5127 — Guide for Ultra Pure Water Used in the Electronics and Semiconductor Industry
1
4.3 JEITA (formerly JEIDA) Standard
EM-3504 (61) — Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
2
4.4 DIN Standard
50438/1 — Determination of Impurity Content in Silicon by Infrared Absorption: Oxygen
3
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 For definitions of terms relating to silicon technology, refer to SEMI M59.
1 Annual Book of ASTM Standards, Vol 11.01, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone: 610-
832-9500, Fax: 610-832-9555, Website:
www.astm.org
2 Japan Electronics and Information Technology Industries Association, 3
rd
floor, Mitsui Sumitomo Kaijo Bldg. Annex, 11, Kanda-Surugadai 3-
chome, Chiyoda-ku, Tokyo 101-0062, Japan, Telephone: 81.3.3518.6434, Fax: 81.3.3295.8726, Website:
www.jeita.or.jp
.
3 Deutches Institut für Normung e.V., standards are available in both English and German editions from Beuth Verlag GmbH, Burggrafenstrasse
6, 10787 Berlin, Germany, Telephone: 49.30.2601-0, Fax: 49.30.2601.1263, Website:
www.beuth.de
.
SEMI MF1239-0305 © SEMI 2003, 2005 3
6 Summary of Test Method
6.1 A representative sample is selected from each group of wafers to be tested.
6.2 The initial value of interstitial oxygen concentration is measured by the infrared absorption method at the
desired points on each wafer.
6.3 The wafers are passed through one of two simulation thermal cycles. Cycle A consists solely of a precipitation
step. Cycle B consists of a nucleation step followed by a precipitation step.
6.4 After the thermal cycle, the oxide film is stripped and the final value of oxygen concentration is measured at the
same points on each wafer using the same technique and instrumentation as was used to determine the initial value.
6.5 The oxygen reduction is determined for each wafer (or for each point on each wafer) tested as the difference
between the initial and final values.
6.6 If all samples have the same initial oxygen concentration (within a narrow range), the average oxygen reduction
for each test condition (such as, group or position on wafer) is computed, and the appropriate comparisons made.
6.7 If the samples have initial oxygen concentrations that cover a relatively wide range, a plot of oxygen reduction
against initial oxygen concentration is made for each group or position. Again appropriate comparisons can be
made.
7 Apparatus
7.1 Infrared Absorption Spectrophotometer, as specified in SEMI MF1188 or DIN 50438, Part 1.
7.2 Resistance Heated Tube Furnace, capable of providing temperatures in the range from 750°C to 1050°C to
±2°C over the length required to contain the load of wafers to be tested. The furnace shall be fitted with the
following:
7.2.1 Gas Manifold — That allows dry oxygen and nitrogen to be mixed at the required ratios and flows, (see Table
1);
Table 1 Thermal Cycle Tests for Oxygen Precipitation in Silicon
Parameter Value
Test A 1050°C for 16 h
Test B 750°C for 4 h followed by 1050°C for 16 h
Furnace Ambient Nitrogen plus 5% dry oxygen
Gas Flow Rate 4.2 ± 0.2 L/min
#1
Push/Pull Temperature 750°C
Push/Pull Rate 25 cm/min
Ramp Up Rate 10°C/min
Ramp Down Rate 5°C/min
#1
For 155 mm diameter tube; for other diameters flow rate should be proportional to the cross sectional area of the tube.
7.2.2 Quartz, Polysilicon, or Silicon Carbide Tube — Of diameter appropriate for the wafers to be tested to isolate
the wafers from external contamination;
7.2.3 Quartz Boats — To hold the wafers during processing;
7.2.4 Loader — To allow controlled insertion of the quartz boat into the hot zone, (see Table 1); and
7.2.5 Laminar Flow Load Station — To permit loading of the wafers without adding contamination to the surfaces.
7.3 Facilities for processing wafers through chem-mechanical polishing, or bright acid etching to provide smooth,
flat surfaces.
7.4 Facilities for dipping the wafers in hydrofluoric acid prior to the oxygen determination in order to remove the
surface oxide film grown during thermal cycling. Suitable protective clothing, acid disposal facilities, and
ventilation shall be provided.