Magma’s YieldManager could make solar ‘rock’!

September 10, 2008

Make no mistake, folks! The EDA guys are getting their act together to penetrate the solar/PV segment!! Magma’s YieldManager is a great example of that effort! Yes, we all know the troubles of the EDA industry as well as of the key players. However, let’s not ignore this initiative from Magma!

Recently, Magma Design Automation Inc. announced the development of a new yield enhancement software system, the YieldManager software system, which is customized for solar fabs to improve conversion efficiency, increase yield and reduce the manufacturing costs of solar cells.

Magma is collaborating with Pegasus Semiconductor-Solar to refine the product specifications and test the new product, based on Magma’s YieldManager.

This is an interesting development, especially from the point of view of the solar/PV industry! Even more significant is the entrance of the EDA community [the one being Synopsys] into solar/PV, a segment, which has witnessed a substantial amount of investments worldwide, and specifically, in India.

It was fun catching up with Ankush Oberai, VP, Failure Analysis Business Unit, Magma Design Automation, in Silicon Valley, to find out more about the YieldManager software system, what it can do for the solar/PV industry, and why Magma decided to venture into an ‘unchartered territory’.

The first and most obvious thing, why YieldManager?

Ankush Oberoi says that in semiconductors, yield impacting parameters which are regularly monitored are mostly extrinsic, i.e., from outside, such as particles, over-exposure, under-exposure and miss-processing. In solar cells, the yield impacting parameters are mostly intrinsic, that is, something built into the solar cell material which can NOT be easily seen. Thus, a different “eye” is needed to see the solar parameters. The “eye” is the YieldManager here!!!

It would NOT be either inspection tools or litho optical proximity correction (OPC) detector. The solar cell efficiency is directly influenced by electro-physics of solar materials. A YieldManger is required to monitor any changes in those efficiency impacting parameters.

The most important parameter is the lifetime of current-generating carriers. As the solar energy generates the “hole-electron” pairs, they are collected separately as electricity.

If the solar material is “dirty” with many crystalline boundaries as in thin film solar cells, the solar generated hole-electrons get pulled into those crystalline boundaries and do not contribute to the electricity generation.

“Thus, if we can find a solar yield management system to detect the very subtle change in carrier lifetime, then we are at home with a greatest Home Run in solar cell business,” he contends.

Given the EDA background, why did Magma decide on a yield management technology?

He adds that yield management technology was acquired by Magma as part of the Knights Technology acquisition in Nov 2006. Magma’s Fab Business Unit (formerly, Knights Technology) is a pioneer (since 1994) in yield management for semiconductor technology.

The product is deployed and used in leading fabs around the world to help manage production wafer yield. Yield management has also been deployed for mask making and LCD productions.

It would be interesting to know how Magma’s new product will allow solar fabs to better monitor all metrology, inspection and performance data throughout the manufacturing process.

Oberoi says: “For Si wafer solar cell, the most important parameter to monitor is the solar conversion efficiency impacting parameters. An example would be a carrier lifetime.

“If the carrier lifetime fluctuates more than normal, the solar Yield Manager will quickly examine all of the key data, i.e., metrology, inspection and performance data, to pinpoint out potential root-causes of the fluctuation problem.”

For thin film solar cell, particles, laser cutting integrity and film thickness uniformity would be main things to monitor. Those data are quite similarly collected, as in semiconductors, and would be monitored as similar ways. The Solar Yield Manager would do well as proven in semiconductors in this case.

Next, it is important to find out how will the YieldManager enable fab operators to identify and correct root causes of solar-efficiency and yield degradation caused by subtle fab processing fluctuations or instability.

According to Oberoi, the carrier lifetime, which could be caused by various factors, is the most critical parameter to monitor for achieving and maintaining the good solar conversion efficiency.

He says: “As the Solar Yield Manager carefully monitors those factors, blindly committing ~400,000 wafers a day can be eliminated, when critical process instability starts appearing and persists. The solar conversion efficiency impacting factors could be monitored differently by different solar fabs.”

Some fabs may not have capabilities to monitor those factors. The Solar Yield Manager would define those metrology and performance tool requirements, when released.

It is also interesting to learn how improving the energy conversion efficiency, reducing the manufacturing costs and increasing the yield of silicon wafer-based solar cells are critical to the growth of the solar market.

Currently, the Si wafer for solar cell costs $2~$2.5/watt due to the severe shortage of Si. The selling price of a solar cell is $3~$3.5/watt, that is, the material cost is 60~70 percent of the solar cell price.

No market or industry would prevail with the 60~70 percent material cost, adds Oberoi. Thus, every milli-watt squeezed out of a solar cell would be very critically important for proliferation of solar industry.

In order to increase the power output of a solar cell, the solar conversion efficiency must be maximized. Once maximized, sustaining the good solar efficiency is the name of the game in the solar cell manufacturing business.

The effective manufacturing cost will be drastically lowered, if bad solar cells with poor solar efficiency is minimally produced. That is, some fabs will use ~400,000 wafers a day to generate ~500 M-Watt a year, whereas some ~450,000 wafers to do the same with poorer solar efficiency.

Innovation in the solar fabrication process must be accelerated, and today, no other enterprise-wide yield enhancement software exists for solar fabs.

Oberoi says: “Solar cell is an old technology, but a very new industry, simply because not enough money was being invested. Now, money is pouring into the solar industry and products like solar Yield will start to appear. It is not known yet that anyone commercially has tried to develop a similar product.”

Global estimate of solar/PV industry
There are several publications with recent estimates. The annual solar cell installation in the world: Germany ~46 percent, Japan ~23 percent, USA ~9 percent, Spain ~6 percent, Italy ~4 percent, the rest of Europe ~1 percent, the rest of Asia, including India and China ~6 percent, and the rest of world ~5 percent in 2006.

Magma is currently in the design and implementation stages of the product and plan to have version 1.0 of the product commercially available in Q1-09. The company has targeted solar fabs based in Asia that are eager for early implementation of the solar yield product.

Right then: those planning or having solar fabs! Now’s the time to test that home run theory with the YieldManager.

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