Background Statement for SEMI Draft Document 5111
New Standard: TEST METHOD FOR SPECTRALLY RESOLVED
REFLECTIVE AND TRANSMISSIVE HAZE OF TRANSPARENT
CONDUCTING OXIDE (TCO) FILMS FOR PV APPLICATION
Notice: This background statement is not part of the balloted item. It is provided solely to assist the
recipient in reaching an informed decision based on the rationale of the activity that preceded the creation
of this document.
Notice: Recipients of this document are invited to submit, with their comments, notification of any relevant
patented technology or copyrighted items of which they are aware and to provide supporting
documentation. In this context, “patented technology” is defined as technology for which a patent has
issued or has been applied for. In the latter case, only publicly available information on the contents of the
patent application is to be provided.
Haze is a common parameter for specifying textured TCO films on glass or amorphous silicon.
This parameter is actually the same a total integrated scatter as specified in SEMI MF1048.
However, it covers only reflective TIS and because haze in the transmissive mode is also desired,
the Photovoltaic Committee is developing a method for measuring haze on materials used in
photovoltaics.
This document will be balloted in cycle 5 of 2011. The results will be discussed at the PV
Electrical & Optical Properties Measurements Task Force and adjudicated by the PV Materials
Committee at their NA Fall meetings in San Jose, California the week of October 24th. Check
www.semi.org/standards for the latest meeting schedule.
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SEMI Draft Document 5111
NEW STANDARD: TEST METHOD FOR SPECTRALLY RESOLVED
REFLECTIVE AND TRANSMISSIVE HAZE OF TRANSPARENT
CONDUCTING OXIDE (TCO) FILMS FOR PV APPLICATION
This specification was technically approved by the Global Photovoltaic Materials Committee. Current
edition approved for publication by the global Audits and Reviews Subcommittee on date tbd. Initially
available at www.semi.org date tbd; to be published date tbd.
1 Purpose
1.1 Transparent conducting oxide (TCO) films used in the photovoltaic industry are textured in order to optimize
light absorption and maximize cell efficiency. Frequently, haze measurements are used to characterize such films.
The required texture usually is not well defined by a single haze result because the relative amounts of low and high
frequency roughness on the surface can both be important. Therefore the haze is frequently determined for a
spectrum of source wavelengths. Then the haze values can often be correlated with useful properties of the material.
1.2 In the PV field, haze is taken as the total integrated reflective or transmissive scatter from the surface of the
sample. The basics of this measurement are covered in SEMI MF1048.
2 Scope
2.1 This test method extends SEMI MF1048 and SEMI PV15 to measurements of reflective and transmissive haze
as a function of source wavelength on TCO films used in the PV industry.
2.2 Reflective haze can be obtained on TCO films deposited on amorphous or other types of silicon.
2.3 Transmissive haze can be obtained in a similar fashion on TCO films deposited on transparent materials, such
as glass.
2.4 Haze is determined as a function of the incident wavelength of the source beam.
2.5 Haze is also determined as a function of the incident angle between the source beam and the film surface normal.
2.6 If desired, it can also be determined at different positions on the sample film.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 Measured haze (or TIS) values change with measurement parameters such as the source wavelength, incident
angle, polarization, and scatter collection regions. As a result comparing haze values found for samples where these
parameters were different is meaningless. Thus, these parameters need to be reported directly, or implied by
identifying the measurement system used for the tests.
3.2 Variations in detector response as a function of the angle of incidence can affect the precision of the
measurement.
3.3 Lack of proper calibration and adjustment of the two detectors makes the ratio of their readings meaningless.
3.4 Defects, such as scratches or pits, that are not characteristic of the surface finish, or contaminants on the surface
can produce scattering that is not characteristic of the texture of the surface.
3.5 Stray background radiation affects the precision of measurement.
3.6 Detector offset voltages affect the precision of measurement.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI M59 –– Terminology for Silicon Technology
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
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SEMI MF1048 –– Test Method for Measuring Reflective Total Integrated Scatter
SEMI PV15 — Guide for Defining Conditions for Angle Resolved Light Scatter Measurements to Monitor the
Surface Roughness and Texture of PV Materials
4.2 ANSI Standard1
ANSI Z136.1 — Safe Use of Lasers
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Acronyms, terms, and symbols related to silicon technology, including most of those in this test method, are
listed and defined in SEMI M59.
5.2 Other Acronym Used in this Test Method
5.2.1 TCO — transparent conducting oxide
6 Summary of Method
6.1 For either reflective or transmissive haze measurement, the scattered beam detector array is mounted a known
distance from the sample surface at a known location on the sample.
6.2 The wavelength of the source beam of light is selected.
6.3 The scattered light and the specularly reflected (or transmitted) light are measured.
6.4 The ratio of the scattered light to the sum of the scattered and specularly reflected (or transmitted) light is
calculated to determine the haze value at that wavelength.
6.5 The haze measurement is repeated for as many values of source wavelength as desired.
6.6 If desired, the sample is moved so that the source light strikes another known location on the sample surface,
and the haze measurement is repeated at each location to map the haze as a function of source wavelength over the
sample surface.
6.7 The results are plotted as a function of source wavelength or position or both.
7 Apparatus
7.1 Haze measurements of TCO films can be made using the total integrating sphere specified in SEMI MF1048.
However, in the PV industry a somewhat simpler apparatus such as that shown schematically in Figure 1 is often
used for reflective and transmissive haze measurements. The incident angle is φiº from the sample surface normal,
where φi can be set to any desired angle. In this figure, the φi are set to 20º for convenience in illustrating the system.
7.2 Light Source — a broadband source is projected through spectrometer transfer optics to have a beam that can be
varied over the desired range of wavelengths. The source beam diameter is 1 mm or less, the beam divergence is 5
mrad or less and the output power is approximately 2 mW. The narrow band source beam passes through an
adjustable mirror to enable its being directed to the top or bottom of the TCO film.
7.2.1 In the case of reflective haze measurement, the source mirror is set at αiº from the surface normal, where, in
Figure 1, αi = ½(90 + βi)º and βi = φi sending the beam to strike the TCO film after passing through the fixed mirror
and the small aperture Ai at the top of the scattered light detector. The reflected light scattered from the film is
collected by the scattered light collector (Ci).
7.2.2 In the case of transmissive haze measurement, the adjustable mirror is rotated ½(90 – αi)º clockwise so that
the beam is deflected along the dashed path in Figure 1 so that the source beam is reflected by the fixed mirror to
pass through the transparent substrate and strike the bottom of the TCO film. Again the transmitted light scattered
from the film is collected by the scattered light collector (Ci).
1
American National Standards Institute, American National Standards Institute, New York Office: 25 West 43rd Street, New York, NY 10036,
USA. Telephone: 212.642.4900, Fax: 212.398.0023, Website: www.ansi.org.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Fixed
Mirror
Fixed
Mirror
Broadband
Source
Spectrometer
Transfer Optic
Narrow
Band
Source
Beam
αi
Chopper
Scattered Light
Collector, Ci
φi
Adjustable
Mirror
Transparent
Substrate
Direct Beam
Detector, Di
Ad
Ai
βi
αi
Textured TCO
Film
φi
Surface
Normal
Fixed
Mirror
Figure 1
Schematic of Apparatus for the Measurement of Reflective or Transmissive Haze
7.3 Scattered Light Collector— equivalent to a reflector type surface that can collect all of the diffuse scattered
light in a collecting angle of 70° or greater relative to the specimen normal and deposit it on the scattered light
detector (not shown in Figure 1).
7.4 Scattered Light Detector (not shown in Figure 1) — a silicon photovoltaic type having a dynamic range of 10 5,
with a sensitive area sufficient to detect all of the collected scattered light. The detector shall have an aperture at the
center that shall subtend an angle of 5° or less at the specimen.
7.4.1 In the reflective haze mode, a second aperture Ad at the top of the scattered light detector allows the reflected
beam to exit past the scattered light collector (Ci) to the direct beam detector, Di.
7.4.2 In the transmissive haze mode, this second aperture Ad at the top of the scattered light detector allows the
transmitted direct beam to exit past the scattered light collector (Ci) to the direct beam detector (Di).
7.5 Fixed Mirrors — two are inserted in the source beam to deflect the beam to the textured TCO film and a third is
inserted to deflect the reflected or transmitted source beam to the direct light detector (Di).
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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7.6 Optical Chopper, in the source narrow band beam, provided with a reference output signal.
7.7 Amplifier, Lock-In Type (not shown in Figure 1), equipped with a preamplifier with a range of gain settings
appropriate for accommodating the range of signals originating from the detector. The amplifier-detector
combination shall have a linear response within ±10% and reproducibility of ±5% over the required range of
measurement.
8 Hazards
8.1 Warning: Lasers with an output power on the order of 1 mW or greater can cause injury to personnel. The
provisions of ANSI Z136.1 should be followed.
9 Sampling
9.1 The number of sample beam wavelengths, M, and the number of measurements, N, to be performed at each
position on the sample shall be agreed to by the parties to the test. Record M and N together with the wavelength
range and interval used.
9.2 The location of each measurement position shall be agreed upon by the parties to the test.
9.3 The number of test specimens and their manner of selection from a given lot shall be agreed to by the parties to
the test.
10 Calibration
10.1 Calibrate the sensitivity of both the direct beam and scattered light detectors over a range of intensities likely
to be met in practice so that the ratio of their readings can be properly made.
11 Test Specimens
11.1 No particular treatment is required for samples to be tested. However, they should be retained in relatively
clean storage areas, so that localized light scatterers arising from surface contamination do not influence the haze
measurement.
12 Procedure
NOTE 1: Some of the items recorded in this procedure may be properties of the apparatus used. Refer to the instruction book for
the apparatus being used to obtain these items or simply record the type of apparatus utilized together with the manufacturer,
model number, software number, etc.
12.1 Position the specimen in the beam a known distance from the scattered light collector and such that the beam
impinges on a specified measurement location of the sample surface at the desired incident angle φi with the surface
normal.
12.2 Record the distance from the sample surface to the nearest points of the scattered light detector so that the
maximum collecting angle can be calculated.
12.3 Select the starting source wavelength and record it as λ1.
12.4 Set the adjustable mirror to measure the reflective haze.
12.5 Record the amount of radiation striking the direct beam detector as Rspr1.
12.6 Record the amount of radiation striking the scattered light detector as Rscr1.
12.7 Reset the adjustable mirror to measure the transmissive haze.
12.8 Record the amount of radiation striking the direct beam detector as Rspt1.
12.9 Record the amount of radiation striking the scattered light detector as Rsct1.
12.10 Select the next desired source wavelength and record it as λ2.
12.11 Repeat ¶¶ 12.4 through 12.10 incrementing the final subscript each cycle and record λi, Rspri, Rscri. Rspti, and
Rscti for each value of source wavelength used. The last source wavelength to be used is λM.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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12.12 If desired, repeat this procedure N times at each agreed upon measurement position on the specimen as
determined in ¶ 9.1 until M sets of measurements have been completed at each of the agreed upon measurement
positions recording λi, Rspri, Rscri. Rspti, and Rscti at each location.
13 Calculations
NOTE 2: The apparatus may record these values internally and present the results as a map of their ratio. If this capability
exists, the calculations in § 13 need not be carried out manually.
13.1 At each location, calculate the haze as the ratio of Rsc to Rsp.
13.2 Prepare a map of the haze values at each measurement position.
14 Report
14.1 The report shall contain the following information as appropriate:
14.1.1 Description of the haze measuring system, including source wavelengths, polarization, incident angle and the
scatter collection regions (see ¶ 3.1 and Note 1)
14.1.2 Date of test.
14.1.3 Operator identification.
14.1.4 Description of each specimen including:
14.1.4.1.1 Specimen number,
14.1.4.1.2 Lot number, if any,
14.1.4.1.3 Substrate material,
14.1.4.1.4 Coating material(s), and
14.1.4.1.5 Vendor.
14.2 Maps of the reflective and transmissive haze values determined at each location for each source wavelength,
15 Precision and Bias
15.1 The precision and bias of this test method have not been determined.
16 Keywords
16.1 haze, PV, TCO film
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determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are
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respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change
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rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of
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and the risk of infringement of such rights are entirely their own responsibility.
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