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Standardizing Chemical Purity Requirements for the PV Industry

Marty Burkhart, Kevin Nguyen, Ralph Cohen

How the SEMI International Standards Program is using industry cooperation to identify and standardize the process gas and liquid chemical purity needs of photovoltaic cell manufacturing

Introduction

Manufacturers involved in making photovoltaic (PV) or solar cells for residential, commercial and industrial electrical energy generation have fallen victim to the alarmingly competitive nature of the business in a short period. This relatively new industrial sector finds itself shoved into an aggressive environment where squeezing and economizing have become the mantra of survival.

The scenario is not unlike other high tech industries, such as semiconductor, where phrases like smarter, cheaper, faster were born. For example, normalized capital investment costs per bit of NAND flash memory production have fallen approximately 100x in the past five years. (Footnote 1)

Similarly, every PV manufacturer is in a race for grid parity, meaning that cost control in every aspect of production must be considered. Measured in US Dollars per watt, the PV industry saw a manufacturing cost decline from $6.07 to $2.70 over the 15-year period from 1990 to 2005. (Footnote 2)

Meanwhile, recent sources are touting less than $1.00 per watt today with 2014 targets in the $0.52 to $0.63 range. (Footnote 3) This now becomes a battleground to wring out every possible cent.

The authors would like to address briefly how standardization efforts in the past have aided semiconductor manufacturing. Correctly identifying material needs prevents over specifying/over paying or under specifying/under performing materials, such as the gases used in production. A parallel can be drawn that such an approach will also ultimately benefit the PV industry as well.

Background

The SEMI International Standards Program was established in 1973 to support the fast growing semiconductor manufacturing industry, creating industry standards developed by suppliers, device manufacturers, safety experts and other stakeholders.

Since inception, SEMI has generated almost 800 Standards and Safety Guidelines contained within 80 topics related to semiconductor manufacturing. Recent years have seen the program expanded to include MEMS and PV.

Drawing on an example of standardization success, since 1975 the cost of one semiconductor transistor has been reduced by a factor of more than 4,000,000. To put this into perspective, consider the Apple iPod. If you use the average cost of a transistor in 1976 and you take the number of transistors inside an iPod, the device today would cost one billion dollars. It would also be the size of a building. (Footnote 4) Much of this decline in size and cost is owed to standardized equipment and process materials. Defined parameters helped propel the industry forward at a rapid pace, both from a standpoint of uniform materials and equipment that work reliably, as well as providing realistic targets for suppliers to compete on cost and offer continuous improvements within the bounds of the end-users’ true needs. (The term "end-user" in the context of this article is intended to mean the worker on the process line who is actually using the gas (or liquid chemical) to make a raw wafer, solar cell or module.)

Early on, PV industry executives voiced concerns with SEMI regarding the lack of agreement on basic manufacturing and materials parameters, recognizing that global standardization activities are a critical component of manufacturing cost reduction and increasing cell efficiency. As such, SEMI began to form teams of industry experts to take standards from the semiconductor library that could be used to address the most critical areas first. (Footnote 5)

The Photovoltaic Gas and Liquid Chemical Purity Taskforce (PVG&LCP)

After determining priorities for standards creation, the SEMI North America (NA) PV Standards Committee authorized the formation of the PV Standards Committee within the SEMI North American PV Group authorized the formation of a task force (TF) dedicated to the area of Gases and Liquid Chemicals Purity. Meeting monthly by phone conference, these industry experts come together in a neutral forum to develop common standards and guidelines beneficial to the PV industry. The TF is comprised of technologists from leading industries that consult, produce, or manufacture solar cells, gases, liquid chemicals, purification components, and ancillary equipment used in PV production. For those unfamiliar with the TF efforts of SEMI, it should be noted that members are encouraged to maintain openness during discussions. However, disclosure of information or proprietary technologies specific to the member’s company or processes is strongly discouraged. Also, the TF is not involved in selling products, discussions on price point, or marketing within the TF meeting. These are forbidden topics. It is a technical forum.

Additionally, the PVG & LCP does not intend to recommend or guide the PV industry in selecting gas or liquid chemical purities needed to produce solar cells. The intent is to provide the industry (end-users and suppliers alike) with a set of written documents for gases and liquid chemicals that can be used to obtain consistent, specified process materials, ultimately bringing the following benefits:

  • Remove the ambiguity in materials supplied to the industry so that the customer gets what is truly needed and the supplier knows what to produce.
  • Provide a level playing field by preventing commercial deception when suppliers meet the nomenclatural intent of the material but not the actual customer's need.
  • Avoid customer/supplier discussions about rejected material not performing as expected
  • Give the end-user the ability to improve the process by adjusting specified material purity levels if deemed advantageous.

Current Status of the PVG&LCP Task Force

The preparation and balloting process for SEMI documents follows a well-defined protocol. After a need is determined, a TF is formed from interested individuals. After the TF meets a few times a rough draft document begins to emerge. Once consensus is reached among the TF members, SEMI will take the document and format it for balloting (either informational or letter ballots) and dispense it to the industry for voting. In the case of letter balloting, "binding" input on the document is solicited from the industry. Following voting on ballots, the comments received are formally handled in the much larger PV committee where any reject votes must be resolved (found to be non-persuasive) prior to publication. At this point, general consensus is reached, but unanimity is not required. Published documents then become the standardization tool for end-users and suppliers.

Working with a variety of members from various disciplines consisting of numerous gas suppliers, one PV manufacturer, two consultants and one analytical lab, the TF has recently created informational and letter balloted documents defining the purity requirements of bulk gas argon, bulk gas nitrogen and bulk gas hydrogen. Bulk gas oxygen, silane and phosphorus oxychloride are currently works in progress. Clean dry air and other needed gases will follow. Voters consisted of a list of registered SEMI members expressing an interest in the PV industry, including end-users and suppliers.

Concerning liquid chemicals, the TF is currently preparing documents for hydrochloric, nitric, phosphoric, and hydrofluoric acids. Consensus within the TF is being developed. Sulfuric acid and others will follow.

Deionized water is also classified as a liquid chemical and its purity is of great importance to PV manufacturing. Our TF has recently developed and released a High Purity Water Guide for letter balloting.

One knowledgeable source and TF member summarizes the concept behind the High Purity Water Guide as follows: “The needs of PV 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.” (Footnote 6)

Cost Effective Materials and TF Participation

SEMI Task Forces have developed a family of standards for semiconductor gas system construction and quality assurance that include SEMI Standard F19, defining parameters for specifying several grades of stainless steel tubing for semiconductor applications, SEMI Standard F78, defining orbital welding methodology, and SEMI Standard F81, defining welding quality assurance, respectively.

The bulk gas purity guidelines being developed for the PV industry have allowable impurities up to several orders of magnitude greater than the corresponding semiconductor industry gases. This is because of the gross geometry of the product and the sensitivity of specific manufacturing steps to contamination. For example sputtering of metal for contact layers or plasma etching of the wafer edge does not require high purity gases but thin film silicon deposition or high temperature diffusion does.

Wherever less pure gases can be used in the process, there is an opportunity, then, to review and edit the semiconductor standards for gas system materials and construction and relax some of the requirements so that they are appropriate for the gas purity outcomes required in PV manufacturing. Some areas to consider are internal surface treatment and cleanliness (electropolished vs. anodic cleaned or mechanically polished), stainless steel grade (316L vs. 304L), fitting type (machined vs. bent), internal tubing roughness, helium leak rates, valve types (diaphragm vs. ball), and joining method (orbital welding vs. compression or crimped).

The outcome of such an exercise would be to provide the PV industry with consensus guidelines reviewed by industry experts that will yield more cost effective installations than those installed using current semiconductor standards.

Companies Involved

Current participating companies in the PVG&LCP TF include Air Products, Air Liquide, Linde, KMG Chemicals, ICL Performance Products, Hi Pure Tech, Parker Hannifin, Matheson-Trigas, Pall, Solar World, Peak Sun Silicon, Mott Corporation, Entegris, Solvay Chemicals and many more. To ensure the development of consensus standards under well-defined democratic procedures, each company has a vote, regardless of its size, as governed by SEMI Regulations.

How to Become a Member

Membership and participation in this TF as well as any other SEMI or SEMI PV TF is free and open to anyone with an interest. A simple membership form is available on the SEMI’s web site. (Footnote 7) Global PV producers/process engineers, tool manufacturers, gas and chemical suppliers, as well as component manufacturers of gas and liquid distribution systems are urgently and continually needed to provide the TF with a well-rounded approach within this important forum. Participation would be greatly appreciated. There are two basic obligations for members; first, be vocal and contribute with remarks during TF meetings and second, vote on SEMI ballots to remain active in the program.

Summary

The photovoltaic industry is expected to grow from $2.3B to ~$15B by 2015. This is an exciting and relatively new industry with much work still to be done before standards and guidelines are fully defined and all possible manufacturing cost reductions are achieved. Fortunately, the PV industry can take advantage of years of SEMI standards as a starting point. The PV Bulk Gas TF expects to finalize guidelines for bulk nitrogen, hydrogen, and argon in early 2010, with more guidelines being released later the same year.

The creation of semiconductor standards in the 1970s paved paths for the semiconductor industry revolution. In the industry’s infancy, technical experts met in countless meetings, exchanged ideas, and agreed on key parameters that provided the foundation. Today, semiconductor chips are in every piece of electronic equipment from cell phones to laptops, to automobiles, just to name a few. Now there is a similar opportunity for involvement with the PV industry while also participating in the green movement. Governments worldwide are developing policies supporting PV with alternative energy incentives. Oil consumption is depleting our fossil fuel reserves and has been shown to be a major contributing factor for global warming.

Using these conditions as the springboard, some particularly significant growth areas are reflected in the expectation that thin-film technologies will take an increasing share of the PV market. (Source: Linx-AEI Consulting). (Footnote 8) Companies and researchers around the world are racing to build more efficient cells while minimizing material cost. Standardization will help improve the chain of communication, reduce cost, and reduce product differentiation.

Footnotes

1 IC Insights Fall Forecast Seminar, (September 2009) Sunnyvale, California.

2. Paula Mint, Principal Analyst, Navigant Consulting PV Services Program

3. “First Solar Goes for Reduction in Manufacturing Cost”, Thin Film Today (1st July 2009).

4. B. Weiss, W. Baylies, M. Burkhart, D. Cook. Manuscript supporting the poster presentation presented at the 34th IEEE Photovoltaic Specialists Conference, Philadelphia, PA , (June 7-12, 2009) "PV Manufacturing Standards - The Path to Yield-up / Cost-down".

5. W. Baylies, M. Burkhart, D. Cook, B. Weiss. “Structuring standards for the photovoltaic manufacturing industry”, Photovoltaics International, 2nd Edition, Fourth Quarter, (2008) pp. 151-154.

6. Private conversation with SubTeam High Purity Water TF Leader Slava Libman, MW Zander, (August 2009).

7. http://dom.semi.org/standards/stdsmbr.nsf/Mapp!openform or www.semi.org/standardsmembership

8. http://www.pv-tech.org/news/_a/linx-aei_consulting_photovoltaics_materials_market_to_top_us15_billion_by_2/

The Authors

Ralph Cohen retired from Intel Corporation in May 2005, completing 20+ years with the company. While at Intel he was engaged in facility design, construction, startup, supplier qualification and management, failure analysis, engineering team management, and recruiting. Design work focused on mechanical systems for wafer fabs, assembly-test plants, and data centers with specialties in bulk gas systems and energy conservation. Cohen graduated with a BS in mechanical engineering from Stevens Institute of Technology with further studies in HVAC and welding including training at Tohoku University. He holds Professional Engineering licenses in Pennsylvania and Oregon. Since retiring, he has established the Ralph M Cohen Consultancy. Marty is also a member of the Gases & Instrumentation Editorial Advisory Board

Kevin Nguyen joined SEMI as a Standards Engineer in 2000. He is now the Manager of NA Standards Committee guiding volunteers to create facilities, gases, silicon wafers, and photovoltaic standards. He holds a B.S. in Chemical Engineer from the University of California, Davis.

Marty Burkhart is the owner of Hi Pure Tech, Inc., providing consulting services and technical support for high-purity products to Georg Fischer Piping Systems. Prior to that, he was employed by Georg Fischer as a technical marketing manager for high-purity products in Switzerland. He also has 13 years experience with Texas Instruments in Dallas, Texas. Currently, Burkhart is the leader of SEMI’s PV Gases and Liquid Chemical Purity Taskforce. He s also a member of Gases & Instrumentation Editorial Advisory Board.

This article was published in the November/December 2009 edition of Gases & Instrumental International Magazine, www.gasesmag.com and is reprinted with permission.