SEMI PV3: Guide for High Purity Water Used in PV Cell Processing
Water is used extensively in the production of photovoltaic (PV) cells and associated manufacturing for all wet processing steps such as rinsing chemical residues from equipment and rinsing of substrate wafers and panels. Overly stringent specifications lead to unnecessarily high investment in equipment and negatively impact profitability, while insufficient specifications adversely impact manufacturing yield. Thus, a standard for water quality is needed to create a common understanding of requirements between High Purity Water (HPW) suppliers and users.
Addressing Water Quality Requirements
Up until recently, there have been no industry standards on water quality for Photovoltaic manufacturing. SEMI PV3-0310, Guide for High Purity Water Used in Photovoltaic Cell Processing, published in March 2010, is the first industry PV water standard. While SEMI F63 and ASTM D5127 have long been used by the semiconductor and electronic industries, the needs of photovoltaic end users differ from those in semiconductor when it comes to high purity water used during production. This is driven by different (lower) sensitivity to water quality parameters and higher sensitivity to facility system cost.
Standards Developed by the PV Industry for the PV Industry
In the course of developing PV3, the SEMI Standards PV Water Working Group, comprised of PV manufacturers, suppliers, engineers and facilities managers, evaluated different qualities of water. This evaluation provided cost consideration, based on the idea that higher quality requirements require additional investment in the treatment process. At the same time, industry feedback was sought via surveying. Input was gathered, discussed and ultimately incorporated into the document. This combination of valuable industry input and the working group’s collaborative assessment resulted in an industry-accepted guideline for high purity water used in photovoltaic cell processing.
SEMI PV3 addresses both High Purity and Standard Purity, which reflect current state-of-the-art PV manufacturing (see below)
Resistivity on-line @ 25°C (Mohm–cm)
High Purity = >17.5
Standard Purity = >10
High Purity is applicable for higher sensitivity PV processes and Standard Purity is targeted for lower sensitivity PV processes. Depending on performance requirements, PV3 may be used to establish performance criteria for purchase of new HPW equipment. Facility engineers may also use this standard to set process control parameters for operating their HPW systems, and process engineers may use PV3 to establish reasonable expectations on supplied HPW in their facilities.
How will this standard provide cost savings or overall economic benefits?
This standard will help optimize HPW quality specifications and as a result will minimize investment in HPW systems. Standardizing water quality helps not only to speed up the decision-making process, but to also standardize the HPW system configuration. Standard configurations will further reduce the cost of HPW systems, as they will not have to be custom made. Additionally, using sufficient specifications will protect manufacturing from adverse yield and quality impacts.
PV Standards Meetings
The European PV Standards Committee recently met in Berlin during the PV Fab Managers Forum (March 7-9), and SEMI recently hosted Standards meetings from March 29-31 at SEMI Headquarters in San Jose, California. In addition to the PV Standards Committee, several other groups, including the PV Materials Task Force (TF), the PV Analytical Test Methods TF, the PV Electrical & Optical Properties TF, the PV Gas & Liquid Chemicals TF, the Minority Carrier Lifetime Working Group (WG), the Transparent Conductive Oxide WG, and the c-Si Cell Specification WG met to review current proposals as well as to chart out future work. Additionally, the Taiwan PV Standards Committee met in late March, while Japan will conduct PV Standards meetings on April 8 at the SEMI Office in Tokyo. See the full calendar of events.
For more information, please contact your local SEMI Standards staff.
Call for Participation
The SEMI PV Group needs your participation. If you are in the PV supply chain, please contact SEMI PV Group International Standards Director James Amano at email@example.com. Over 71 percent of companies participating in Standards Committees believe that it helps them anticipate future market requirements! Participation is free, but registration is required.
Standards Watch, April 2010