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4805
Background Statement for SEMI Draft Document 4805B
NEW STANDARD: SPECIFICATION FOR VIRGIN SILICON FEEDSTOCK MATERIALS FOR PHOTOVOLTAIC APPLICATIONS
Note: 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.
Note: 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.
The increasing number of players in the market for Si feedstock materials has introduced a wide variety of material grades. This requires considerable efforts of the parties involved to achieve a common understanding of the material specifications and the impacts of the different materials on the resulting PV product quality and performance. Standardized specifications of these feedstock materials are highly desirable. Therefore the PV Committee has approved in its meeting in Hamburg on September 22, 2009 a new Task Force, the PV Si Materials TF, and development of a new standard, a specification for Si feedstock for photovoltaic applications. This document was developed in between September 2009 and March 2010 by a working group that included the three largest suppliers of poly-Si as well suppliers providing metallurgically refined Si. This group had three phone conferences and the TF two face-to-face meetings in Berlin in March 2010 and in Munich in June 2010. The views of the European group on negatives and comments submitted from Japan were communicated in a phone conference with Japan in June 2010, resulting in a new proposal from Japan. The current version of doc 4805 addresses most negatives and comments obtained during the ballot and it includes the Japanese proposal with slight modifications.
Document 4805 was approved for ballot in cycle 3 2010 at the meeting of the NA PV Committee in Milpitas in March 2010. The ballot results of doc 4805 were adjudicated by the PV Committee in its meeting in San Francisco on July 14, 2010 and the document failed. Immediate reballoting of the document modified according to the negatives and comments obtained during the ballot was also approved in this meeting. Adjudication of this ballot in cycle 5, 2010, occurred at the PV Committee meeting in Dresden in October 2010 in conjunction with SEMICON Europe, where doc 4805 failed again. Immediate re-ballot of the document, modified according to the ballot negatives and comments, was approved for cycle 1 in 2011, to be adjudicated at the next meeting of the PV Committee in Berlin in March 2011. Check www.semi.org/standards for the latest meeting schedule.
For question on the ballot, contact SEMI Staff, Kevin Nguyen at
SEMI Draft Document 4805B
NEW STANDARD: SPECIFICATION for VIRGIN Silicon Feedstock materials for photovoltaic applications
1 Purpose
1.1 Silicon is one of the key materials in the growing photovoltaic (PV) industry. Solar cells made of silicon will be manufactured for many years to come. New parties supplying or purchasing Si feedstock materials are entering this industry.
1.2 The need for higher volumes and more cost efficient feedstock Si triggered development of metallurgical refining methods. In addition new methods modifying the original Siemens process were investigated and were introduced in high volume manufacturing. In parallel to the development of refining methods a wide variety of crystallization techniques and solar cell designs, each requiring specific material properties, were investigated by industry and research organizations. A multidimensional parameter space would be necessary to describe all the relations between feedstock material quality, single and multicrystalline ingots and finally solar cell performance. These would result in a multitude of interface problems, inhibiting the relations between suppliers and their customers, that is not appropriate for a high volume and fast growing industry.
1.3 Standardized specifications for Si feedstock materials are expected to reduce these interface problems and to enable a common understanding of material properties and terms, allowing reliable manufacturing of ingots of solar cells and benefiting all parties.
2 Scope
2.1 This specification covers virgin silicon feedstock materials produced by CVD processes, metallurgical refining processes or other processes. CVD processes include the so-called Siemens process, fluidized bed processes, powder processes and other processes using distilled silane or halosilane compounds.
2.2 These specified materials are intended for growing of single crystalline ingots and casting or other methods of growing multicrystalline Si, used for producing Si wafers for solar cells.
2.3 This specification is not intended for material used for manufacturing thin film solar products such as amorphous or micromorphous Si products, but it may be used if it is appropriate for the specific application.
2.4 This specification only applies to virgin silicon feedstock and not to scrap or waste material coming from the semiconductor industry.
2.5 This specification is also not intended for specifying material blends, although it may be used as a guideline for melts from blended materials.
NOTICE: SEMI standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the user of this document to establish appropriate safety and health guides and determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 None
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI M44 –– Guide to Conversion Factors for Interstitial Oxygen in Silicon
SEMI MF28 –– Test Method for Minority Carrier Lifetime in Bulk Germanium and Silicon by Measurement of Photoconductivity Decay
SEMI MF84 –– Test Method for Measuring Resistivity of Silicon Wafers with an In-Line Four-Point Probe
SEMI MF391 –– Test Method for Minority Carrier Diffusion Length in Extrinsic Semiconductors by Measurement of Steady-State Surface Photovoltage
SEMI MF397 –– Test Method for Resistivity of Silicon Bars Using a Two-Point Probe
SEMI MF723 –– Practice for Conversion between Resistivity and Dopant or Carrier Density for Boron-Doped, Phosphorous-Doped, and Arsenic-Doped Silicon
SEMI MF1188 –– Test Method for Interstitial Oxygen Content of Silicon by Infrared Absorption with Short Baseline
SEMI MF1391 –– Test Method for Substitutional Atomic Carbon Content of Silicon by Infrared Absorption
SEMI MF1528 — Test Method for Measuring Boron Contamination in Heavily Doped n-Type Silicon Substrates by Secondary Ion Mass Spectrometry
SEMI MF1535 –– Test Method for Carrier Recombination Lifetime in Silicon Wafers by Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance
SEMI MF1389 –– Test Method for Photoluminescence Analysis of Single Crystal Silicon for III-V Impurities
SEMI MF1630 –– Test Method for Low Temperature FTIR Analysis of Single Crystal Silicon for III-V Impurities
SEMI MF1708 –– Practice for Evaluation of Granular Polysilicon by Melter Zoner Spectroscopies
SEMI MF1723 –– Practice for Evaluation of Polycrystalline Silicon Rods by Floatzone Crystal Growth and Spectroscopy
SEMI PV1 — Test Method for Measuring Trace Elements in Silicon Feedstock for Silicon Solar Cells by High-Mass Resolution Glow Discharge Mass Spectrometry
SEMI PV10 — Test Method for Instrumental Neutron Activation Analysis (INAA) of Silicon
4.2 ISO Standard[1]
2859 — Sampling procedures for inspection by attributes
4.3 DIN Standard[2]
50451-3 — Testing of materials for semiconductor technology – Determination of traces of elements in liquids – Part 3: Aluminum (Al), cobalt (Co), copper (Cu), sodium (Na), nickel (Ni) and zinc (Zn) in nitric acid by ICP-MS.
51008-2 — Inductively coupled plasma mass spectrometry (ICP-MS) – Part 1: Principles and definitions.
4.4 ANSI/ASQ[3]
Z1.4-2008 — Sampling Procedures and Tables for Inspection by Attributes
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
(Refer to SEMI’s Compilation of Terms (COT) for a list of the most current terms and their definitions.)
5.1 Abbreviations and Acronyms
5.1.1 HRTEM –– high resolution transmission electron microscopy
5.1.2 ICP-OES –– inductively coupled plasma optical emission spectroscopy
5.1.3 NAA –– neutron activation analysis
5.1.4 SEM-EDX –– scanning electron microscopy- energy dispersion x-ray spectroscopy
5.1.5 XRF –– X-ray fluorescence
5.2 Definitions
5.2.1 Chips, polysilicon ––irregularly shaped pieces of polysilicon with a largest dimension less than approximately 50 mm.
5.2.2 Chunks, polysilicon, also called lumps — lumpy polysilicon of non-spherical shape with irregular surface features. The polysilicon chunks have dimensions typically up to 250 mm.
NOTE 1: Chips as well as chunks are generated by crushing poly-Si rods or pmg-Si bricks. There is no clearcut size limit between them, chips are usually the smaller pieces and chunks the larger ones.
5.2.3 CVD processes
5.2.3.1 Fluidized bed process — decomposing distilled silane or a halosilane compound in a fluidized-bed reactor by thermolysis to create polycrystalline granules.
5.2.3.2 Powder process — homogeneously decomposing distilled silane or a halosilane compound in a reactor by thermolysis to create Si powder.
5.2.3.3 Rod CVD process (Siemens process) — decomposing distilled silane or a halosilane compound in a rod deposition reactor (Siemens reactor) by thermolysis to create fine grained polycrystalline Si (poly-Si) in the form of rods.
5.2.4 Granules, polysilicon, also called beads or pellets — approximately spherical particulate polysilicon produced in a fluidized bed reactor with a size of typically 0.1 mm to 10 mm.
5.2.5 Halosilanes –– silanes, in which one or more hydrogen atoms are replaced by halogen atoms, such as SiHCl3 or SiHBr3.
5.2.6 Metallurgical grade Si (mg-Si) — silicon chunks of irregular shapes with a typical purity of 98 % or more Si. Mg-Si is obtained by carbothermal reduction of lumpy SiO2 in submerged electric arc furnaces. It is the raw material for metallurgical refining processes.
5.2.7 Powder, polysilicon, also called fines — polysilicon particles with a maximum dimension ≤500 µm.
NOTE 2: Powder and granule differ with respect to bulk density and morphology. Powder typically has lower density and dendritic like growth structure and may aggregate to form larger particles.
5.2.8 Purified metallurgical grade Si (pmg-Si), also called upgraded metallurgical grade Si (umg-Si) — metallurgical silicon that is purified by applying metallurgical processes to Si, such as slagging, filtering, melting with subsequent oriented solidification, leaching or etching.
5.2.9 Rod, polysilicon — cylindrical or partially cylindrical piece of polysilicon, with a weight typically > 5 kg.
5.2.10 Silane –– SiH4, starting material for 5.2.3.1, 5.2.3.2, 5.2.3.3.
5.2.11 Trichlorosilane (TCS) –– SiHCl3, starting material for 5.2.3.1, 5.2.3.2, 5.2.3.3.
NOTE 3: TCS and silane are obtained from a reaction of HCl with mg-Si followed by purifying the volatile compounds by distillation.
6 Ordering Information
6.1 Purchase orders for Si feedstock materials furnished to this specification shall include the following items. These items are shown in Table 1 together with check boxes, if applicable, for selecting the required characteristic. Open entries, indicated by “____”, have to be filled with numbers and appropriate units.
· General Characteristic, specifying manufacturing method, dopants and co-dopants.
· Chemical Characteristics, quantifying acceptable concentrations of acceptors, donors, carbon, and metals as well as other of other impurities.
· Dimensional Characteristics, defining the morphology, size and weight of the product.
· Surface Characteristics, specifying the surface appearance and oxide layer thickness.
· Packaging, specifying material and size of containers.
· Statistical Acceptance Characteristics, specifying test method, sample size and acceptance criteria for qualifying the product.
· Documentation, defining number of certificates and their content.
6.2 Additional items may be specified optionally in addition to those listed above.
6.3 In all cases, it is essential that all choices for the items specified be made in order not to have unspecified parameters that would lead to surprises between supplier and customer.
6.4 In addition, the purchase order must indicate the test method to be used in evaluating each of those items for which alternate test procedures exist.
Table 1 Specification Format for Order Entry
Part 1 General Information
ITEM / INFORMATION / Date: /Customer Name
Purchase Order Number
Line Number
Item Number
General Specification Number
Revision Level
Part Number/Revision
Part 2 Silicon Feedstock Materials for Photovoltaic Solar Cells
ITEM / SPECIFICATION / MEASUREMENT METHOD#1 /1 / General Characteristics
1.1 / Manufacturing Method / [ ] CVD-poly; [ ] pmg-Si; [ ] other (specify): ____; [ ] not specified
1.2 / Acceptors / [ ] B; [ ] Al; [ ] other (specify): ______
1.3 / Donors / [ ] P; [ ] As; [ ] Sb; [ ] other (specify):______
1.4 / Excess Charge Carrier Lifetime / [ ] specify:____µsec; [ ] not specified / [ ] SEMI MF28#2
[ ] SEMI MF391#2
[ ] SEMI MF1535#2
[ ] other (specify):______
2 / Chemical Characteristics
2.1 / Acceptor Concentration / [ ] category I, tolerance for donors: (specify)_____ppba,
tolerance for acceptors: (specify)______ppba
[ ] category II, target for donors :(specify)____ppba, target for acceptors: (specify)______ppba
[ ] category III, target for donors : (specify)____ppba, target for acceptors: (specify)______ppba
[ ] category IV, target for donors : (specify)____ppba, target for acceptors: (specify)______ppba
[ ] not specified / [ ] SEMI MF84#2 with SEMI MF723
[ ] SEMI MF397#2 with SEMI MF723
[ ] SEMI MF1389#2
[ ] SEMI MF1528
[ ] SEMI MF1630#2
[ ] SEMI PV1
[ ] DIN50451-3
[ ] ICP-MS
[ ] SIMS
[ ] other (specify):______
2.2 / Donor Concentration / [ ] SEMI MF1389#2
[ ] SEMI MF1630#2
[ ] SEMI PV1
[ ] ICP-MS
[ ] SIMS
[ ] other (specify):______
2.3 / Oxygen Concentration / [ ] GFA
[ ] SEMI MF1188#2 with SEMI M44
[ ] SIMS
[ ] other (specify):______
2.4 / Carbon Concentration / [ ] SEMI MF1391#2
[ ] GFA
[ ] SIMS
[ ] other (specify):______
2.5 / Total Transition and Post-Transition Metal Concentration / [ ] SEMI PV1
[ ] DIN50451-3
[ ] DIN51008-2
[ ] ICP-MS
[ ] SEMI PV10
[ ] SIMS
[ ] other (specify):______
2.6 / Total Concentration of Alkali and Earth Alkali Metals / [ ] ICP-MS
[ ] ICP-OES
[ ] SIMS
[ ] other (specify):______
2.7 / Other Element Concentration / [ ] SEMI MF1528
[ ] SEMI PV1
[ ] DIN50451-3
[ ] ICP-MS
[ ] SIMS
[ ] other (specify):______
2.8 / Total Hydrogen Concentration#3 / [ ] SIMS
[ ] other (specify):______
2.9 / Total Chlorine Concentration#3 / [ ] GFA
[ ] XRF
[ ] SIMS
[ ] other (specify):______
2.10 / Total Al Concentration#4 / [ ] specify: ______ppba; [ ] not specified; / [ ] SEMI MF84#2 with SEMI MF723
[ ] SEMI MF397#2 with SEMI MF723
[ ] SEMI MF1389#2
[ ] SEMI MF1528
[ ] SEMI MF1630#2
[ ] SEMI PV1
[ ] DIN50451-3
[ ] ICP-MS
[ ] SIMS
[ ] other (specify):______
2.11 / Exceptions#5 / [ ] specify: ____; [ ] none
3 / Dimensional Characteristics
3.1 / Shape / [ ] chips; [ ] chunks; [ ] rods; [ ] granules; [ ] powder; [ ] bricks; [ ] lumps;
3.2 / Size / Rod diameter: ____ mm
Rod length: ____ mm
Brick length: ______mm
Brick width: ______mm
Brick height: ______mm
3.3 / Remarks
4 / Surface Characteristics
4.1 / Surface Preparation / [ ] cleaned; [ ] etched; [ ] as grown; [ ] other(specify):______
[ ] not specified
4.2 / Surface Appearance / gray clean dry surfaces, foreign material not allowed, low amount (< 1 % of total weight) of brownish amorphous Si / Physical audit
4.3 / Oxide Layer Thickness / for powders only / [ ] GFA
[ ] HRTEM
[ ] SEM-EDX
[ ] SIMS
5 / Packaging
5.1 / Packaging Method / [ ] dust free; [ ] inert atmosphere;
[ ] single/double plastic bags, inside cardboard boxes or barrels, or in lined bigbags
[ ] other: (specify)______
5.2 / Shape of container / [ ] barrel; [ ] box; [ ] other: (specify)______
5.3 / Material of Container / [ ] specify:______
5.4 / Labeling of Container / [ ] supplier; [ ] product type; [ ] lot no.; [ ] shipment date;
[ ] safety notes; [ ] other (specify): ____
6 / Statistical Acceptance Criteria
6.2 / Sampling Rate / Sample size:______
Non-conforming percentage: _____
Inspection level: _____ / [ ] ISO 2859
[ ] ANSI/ASQ Z1.4 – 2008
7 / Documentation
7.1 / Amount of Documents / Number per shipment: ____
7.2 / Type of Document(s) / Certificate of Compliance or Certificate of Analyses with [ ] lot no.; [ ] type no.; [ ] specification no.; [ ] order no.; [ ] analysis results; [ ] machine readable
#1 Method and details of it have to be agreed upon between user and supplier if non-standardized measurement methods are specified.