Background Statement for SEMI Draft Document 5074

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Background Statement for SEMI Draft Document 5074

NEW STANDARD: SPECIFICATION FOR FRONT SURFACE MARKING OF PV SILICON WAFERS WITH TWO-DIMENSIONAL MATRIX SYMBOLS

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.

Increasing pressure on manufacturing cost for solar cells requires a tighter quality control for improving yield. Therefore a mark on the wafers is required for being able to track individual wafers through the manufacturing process and to trace their process history as is practice in the semiconductor industry. Such a mark should be standardized in order to reduce diversity of marks and corresponding detrimental impact on equipment and manufacturing cost.

Therefore a PV Wafer Traceability TF was set up in Berlin on 09.03.2010,and a corresponding SNARF was submitted at the meeting of the PV Committee in Berlin on 09.03.2010,and approved. In its meeting on June 10, 2011, the PV Automation Committee approved the ballot for cycle 5 in 2011. Ballot results will be reviewed by the PV Wafer Traceability TF and adjudicated by PV Automation Committee during their meetings in conjunction with SEMICON Europe in Dresden, Germany, in October 10-13, 2011. Check for the latest meeting information.

If you need further assistance, or have questions, please do not hesitate to contact Kevin Nguyen, SEMI Standards HQ by phone at 1.408.943.6900 or by email at .

SEMI Draft Document 5074

NEW STANDARD: SPECIFICATION FOR FRONT SURFACE MARKING OF PV SILICON WAFERS WITH TWO-DIMENSIONAL MATRIX SYMBOLS

1 Purpose

1.1 A prerequisite for quality and process control in manufacturing of silicon wafers and solar cells is the traceability and track ability of the individual wafers.

1.2 The current specification defines a mark containing a data matrix code (DMC) that will allow to uniquely identifying wafers throughout the manufacturing process chain of solar cells and solar modules and their complete life cycle.

1.3 The specified mark can be easily applied and read, and is designed for stability throughout all solar cell and module manufacturing steps. Negative effects for this type of laser mark, such as increase of wafer breakage or reduction solar cell efficiency, have not been found in careful investigations performed on a large number of wafers and solar cells. This mark is independent of the positional orientation of the wafer.

1.4 Marks are widely used for identifying tracking and tracing wafers in the semiconductor industry. Therefore equipment for applying and reading marks is easily available.

1.5 An additional advantage of a unique wafer mark is product security for producers and users of wafers and solar cells with respect to fraud, theft and counterfeiting.

2 Scope

2.1 This specification defines the geometric and spatial relationships and content (including the error checking and correcting code) of a mark consisting of a rectangular two-dimensional (2-D), machine-readable, binary data matrix code symbol for marking of square or pseudo-square mono- and multicrystalline silicon wafers for photovoltaic application.

2.2 The format and algorithms of this code are based on two-dimensional symbols as specified in ISO/IEC 16022.

2.3 The mark is applied to one as-cut surface of a wafer on the later-to-be front surface of the solar cell.

2.4 One up to four identical marks with the exception of their orientation may be applied to one single wafer.

2.5 Although this specification does not specify the marking techniques that may be employed when complying with its requirements, it is assumed that the symbol will be obtained by laser scribing of the individual dots.

2.6 The mark is applicable to all wafers sizes.

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 Referenced Standards and Documents

3.1 SEMI Standards

SEMI M12 — Specification for Serial Alphanumeric Marking of the Front Surface of Wafers

SEMI MF728 –– Practice for Preparing an Optical Microscope for Dimensional Measurements

3.2 ISO/IEC Standard[1]

ISO/IEC 16022 — International Symbology Specification – Data Matrix Number

3.3 Other Documents

SEMI AUX001— List of Wafer Supplier Identification Codes

NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.

4 Terminology

(Refer to SEMI’s Compilation of Terms (COT) for a list of the most current terms and their definitions.)

4.1 Abbreviations and Acronyms

4.1.1 DMC — data matrix code

4.2 Definitions

4.2.1 alignment bar, of a data matrix code symbol — a solid line of contiguous filled cells abutting a line of alternately filled and empty cells [ISO/IEC 16022].

4.2.2 binary values — a dot in the wafer surface indicates the binary value 1. The absence of a dot, or a smooth surface surrounding a cell center point indicates the binary value 0.

4.2.3 border column — the outermost column of a data matrix code symbol. This column is a portion of the finder pattern.

4.2.4 border row — the outermost row of a data matrix code symbol. This row is a portion of the finder pattern.

4.2.5 cell of a data matrix code symbol — the area within which a dot may be placed to indicate a binary value.

4.2.6 cell center point, of an array — the point at which the centerline of a row intersects the centerline of a column.

4.2.7 cell spacing, of an array — the (equal) vertical or horizontal distance between the cell center points of contiguous cells.

4.2.8 center line, of a row or column — the line positioned parallel to, and spaced equally between, the boundary lines of the row or column.

4.2.9 central area, of a cell — the area enclosed by a circle centered at the cell center point; used by code readers to sense the binary value of the cell.

4.2.10 data matrix code symbol — a two-dimensional array of square cells arranged in contiguous rows and columns. The data region is surrounded by a finder pattern [ISO/IEC 16022].

4.2.11 dot — a localized region with a reflectance which differs from that of the surrounding surface.

NOTE 1:To assure reading efficiency, a minimum contrast of 30% is required between the reflectance value of a dot and the surrounding wafer surface. Various densitometers can provide such measurements nondestructively.

4.2.12 dot misalignment, within a cell — the distance between the physical center point of a dot and the cell center point.

4.2.13 finder pattern, of a data matrix code symbol —a perimeter to the data region. Two adjacent sides contain dots in every cell; these are used primarily to define physical size, orientation and symbol distortion. The two opposite sides are made up of cells containing dots in alternate cells [ISO/IEC 16022].

4.2.14 reference point, of a data matrix code symbol —the physical center point of cell used to identify the physical location of the symbol on the object being marked with the symbol.

4.2.15 reading window –– an area on a wafer in which the dot matrix symbol(s) have to be placed, in order to be read by a reader.

4.2.16 wafer center point — a point on a square or rectangular wafer surface defined by the intersection of the diagonals of the square or rectangle.

5 Ordering Information

5.1 Checklist — Purchase orders for wafers furnished to this specification shall include the following items:

• Number of data matrix symbols per wafer

6 Requirements

6.1 Data Matrix Code Layout

6.1.1 Each data matrix shall consist of a square array of cells of 14 rows and 14 columns with alignment bars as defined in ISO/IEC ISS 16022.

6.1.2 One border row and one border column shall contain a dot in each cell. These are identified as the primary border row and the primary border column. These are used by the code reader to determine the orientation of the matrix. They are also referenced to as “finder pattern”, as shown in figure 2.

6.1.3 The opposing (secondary) border row and column shall contain dots in alternating cells, also reverenced to as “alignment pattern” , as shown in figure 2

6.1.4 For these square matrix code symbols, the reference point of the symbol shall be the center point of the dot matrix symbol.

6.2 Content of the Data Matrix Code Symbol

6.2.1 Each square data matrix code symbol shall contain twelve message characters,together with the error checking and correcting (ECC200) code characters, encoded in accordance with ISO/IEC ISS 16022.

6.2.2 The message characters may include the following: A–Z, 0-9. These characters constitute the SEMI OCR Character Set except for the period (.) and dash (-); this is the similar character set as specified in SEMI M12. These characters are also included in the set designated as "primarily upper case alphanumeric" in ISO/IEC 16022, in Table 5 and Annex J. The twelve message characters shall contain following elements, as detailed in figure 3:

6.2.2.1 a vendor-assigned numeric two-character code identifying the year of manufacturing,

6.2.2.2 a switch code to C40 encoding

6.2.2.3 a alphanumeric two-character vendor identification code (according to SEMI AUX001),

6.2.2.4 a 7-character code identifying and distinguishing the individual wafer within a yearly production of a specific vendor.

6.2.2.4.1 This 7 character can be designed to be a unique, serial number or could include information about ingot, brick and the respective wafer position in it.

6.3 Dimensional requirements (Table 1, figure1 and figure 2)

6.3.1 Data matrix

6.3.1.1 The spacing of the cells (repetitive cell distance) shall be 110 +/- 10 µm center to center.

6.3.1.2 The nominal shape of the dot produced in the matrix shall be circular with its diameter of 90 +/-10 µm

6.3.1.3 The depth of the dots shall be in the range of 5 – 30 µm.

6.3.2 Location of the Data Matrix Code Symbol

6.3.2.1 With the wafer positioned front surface up and its edges parallel to the axes of a right-handed Cartesian coordinate system, the origin of which is at the center of the wafer, the data matrix code symbol shall be located as specified below.

6.3.2.2 Each 14 by 14 dots DMC symbol shall be placed entirely inside a reading window, a square field of a size of 12 * 12 mm2, the codes shall keep the required distance according to ECC200 from each other and from the outer limit of the reading window to cope with wafer position tolerances at reading and therefore increase reading –margins.

6.3.2.3 The outer row or column (finder pattern or alignment pattern) of the dot matrix symbol(s) shall be positioned at a distance of min 1.8 mm from both center lines of the coordinate system.

6.3.2.4 The edges of the DMC shall be oriented parallel to the edges of the wafer.

6.3.2.5 The center points of the reading window shall be positioned at the center of the wafer.

6.3.2.6 The alignment bars of the DMC shall be oriented parallel to the axes of the Cartesian coordinate system.

7 Test Methods

7.1 No standardized test method currently exists for verifying the dimensions, encodation and mark quality of the DMC. Some of these metrics can be checked with a calibrated measurement microscope, video set-up or surface profiler.

8 Certification

8.1 A certificate identifying the wafer manufacturer, reporting the year of manufacturing and listing all wafers in the shipment shall be sent with each shipment of wafers marked with the DMC.

Table 1 Dimensional Requirements

Figure 1

Details of a Cell and aDot

Figure 2

Dimension of the 14x14DMC, Finder and Alignment Pattern

Figure 3

Content of the Data Matrix Code Symbol

Figure 4

Example of Code Placement Inside the Reading Window

NOTICE:Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The determination of the suitability of the Standard or Safety Guideline 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. Standards and Safety Guidelines are subject to change without notice.

By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of this Standard or Safety Guideline 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.

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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