Water is used extensively in the production of photovoltaic (PV) cells and associated manufacturing for all wet processing steps such as removing chemical residues from equipment and rinsing of substrate wafers and panels. Too stringent specifications will lead to unnecessarily high investment of equipment and impact the profitability risk. On the other hand, insufficient specifications will impact manufacturing yield. Thus, standardizing water quality is needed to set a common understanding and requirements between High Purity Water (HPW) suppliers and users.

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. SEMI F63and ASTM D5127have always been used by Semiconductor and Electronic industries. However, the needs of photovoltaic end-users’ requirements 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.

NA PV Water Working Group, comprised of members from PV manufacturing, suppliers, engineers and facilities managers, evaluated different qualities of water. This evaluation provides cost consideration, based on the idea that higher quality requirements require additional investment in the treatment process. At the same time, industry’s feedback was sought via surveying. Inputs were gathered, discussed and ultimately incorporated into the document. A combination of valuable industry inputs and the working group’s collaborative assessment resulted in an industry accepted guideline for high purity water used in photovoltaic cell processing.

SEMI PV3-0310 addressed 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 known for higher sensitivity PV processes and Standard Purity is targeted for less sensitivity PV processes. Depending on performance requirements, PV3-0310 may be used to establish performance criteria for purchases of new HPW equipment. Facility engineers may also use this standard to set process control parameters for operating their HPW systems. Process engineers may also use this to establish a reasonable expectation for supplied HPW in their facilities.

PV Group, The Grid – March 2010

This standard will help to optimize HPW quality specifications and as a result it will optimize and minimize investment in the HPW system. Standardizing water quality helps not only to speed up the decisions, but also standardize the HPW system configuration. Standard configurations will even further reduce the cost of the HPW system, since they will not have to be tailor made. Using adequate specifications will protect manufacturing from yield and quality impacts.

Upcoming PV Standards Meeting

SEMI is hosting NA PV Standards meetings during our Spring meetingsat the end of March. In addition to technical committee meeting, several task forces including PV Materials, PV Analytical Test Methods, PV Electrical & Optical Properties, PV Gas & Liquid Chemicals, Minority Carrier Lifetime, Transparent Conductive Oxide, and c-Si Cell Specification will meet on Tuesday and Wednesday, March 30-31. Come and engage in technical discussions challenging the PV industry. Also, a 2 hour Standards reception at SEMI HQwill be held on Monday night for industry experts to network. Detailed schedulesand registration are available.

For other regional meetings, Europe PV Standards recently met in Berlin during PV Fab Managers Forum. Highlights of that meeting are expected to be reported shortly. Taiwan PV technical Standards committee will also meet later this month, while Japan will conduct their set of PV Standards meetings on April 8 at SEMI Office in Tokyo. See the full calendar of events.

For more information, please contact Kevin Nguyen at knguyen@semi.org, or your local SEMI Standards staff.