Intellectual Property and Technology Space

1. Intellectual Property and Technology Space Sathya KV Edward Graef Zhenhua Li Katrina Geren

2. “Fabrication of polycrystalline silicon film by nano-aluminum induced crystallization of amorphous silicon”

3. Brief Summary of Invention http://www.zyn.com/flcfw/fwtproj/SILICON.JPG Explore the Intellectual Property and Technology Space surrounding a process recently invented by Dr.Li Cai, Dr.Min Zhou, and Dr.William Brown at the University of Arkansas. Filed in 2007. Still pending. The application of this process to solar cells is of primary interest. Low temperature procedure for fabricating large grain polycrystalline silicon (polysilicon) by nano-aluminium induced crystallization of amorphous silicon

4. Polysilicon Polysilicon is a solid material which consists of many small silicon crystals. Older processes require very high temperatures which exclude the use of many low cost substrates. Widely used in a multitude of semiconductor industries. Advantages of introducing aluminum into silicon: Reduces the temperatures at which the amorphous silicon can be crystallized. Used in fabricating photovoltaic and photoelectronic devices Use in manufacturing thin film transistors, resistors and display panels. Smoother polycrystalline film http://news.softpedia.com/images/news2/The-Fastest-Silicon-Based-Optoelectronic-Chips-1.jpg

5. PROCESS • Step 1: 1-3μm thick silicon dioxide layer grown on silicon wafer. • Step 2: 5-200nm thick amorphous silicon grown on silicon dioxide using PECVD. PECVD parameters: RF power -15W Chamber pressure - 0.5Torr Substrate temperature - 250°C SiH4 flow rate of 85sccm • Step 3: 5-100nm thick aluminum grown on amorphous silicon using metal evaporation. • Step 4: Annealing at temperature range 50-450 ºC .

6. Large Grain p-Si crystals Aluminum Thin Film Heat a-Si:H p-Si doped with Al PROCESS • Step 5:Aluminum patterned in four steps: • a photoresist layer is spin coated on the aluminum layer • a desired pattern is formed on the photoresist layer by the photolithographic process • the uncovered aluminum layer is thinned according to the desired pattern making use of chemical process • the remaining photoresist layer is etched off leaving behind the remaining portion of the aluminum layer.

7. CLAIMS Key components - silicon dioxide buffer layer, the thickness of the aluminum layer, and the ramp-up time and temperature of the annealing surface. • Strengths • Claim 16 - patterning the aluminum layer and annealing the structure in the presence of N2 . • Similar to the previous method of aluminum induced crystallization but has a provided a significant improvement in the area of grain size. • No significant improvement in the technology but the result has been improved significantly. The improvement in the grain size should allow this patent to be granted. • Weaknesses • Claim 12 - the ramp-up time required to crystallize the polysilicon from the amorphous silicon. This temperature theoretically could be used statically to achieve the same results as the variable temperature in the patented process without infringing upon this patent. • Differences consist almost entirely of the ramp-up time and the thickness of the aluminum catalyst layer.

8. Comparative Patent Technology Ed Graef

9. Competitive Patented Technology • Several patents exist that could expand the field beyond the capabilities of the U of Arkansas technology. • No infringement of patents exists, though one uses the same reaction as the U of Arkansas (U of A) technology.

10. Outline • Recap of U of A technology • Poly-Si using Al electrode • Weaknesses • Poly-Si using laser annealing • Weaknesses • Poly-Si using a-Si:H melting • Weaknesses • Conclusions

11. Large Grain p-Si crystals Aluminum Thin Film Heat p-Si doped with Al a-Si:H U of A patent pending technology • Uses a thin film of Al to activate smaller # of grain sites • Turns a-Si:H into poly-Si with a p-type doping gradient. • Performs this at low temperatures (<450°C) • Capable of producing 1mm grain size • Low production cost

12. Al Electrode p-Si area with Al as dopant A-Si:H first layer Poly-Si using Al electrode • Very similar to U of A technology. • Instead of thin film it uses small electrode for grain control. • Can create a minimum grain size of ~1.0μm at lower than 500°C. • Grows columnar grains on the order of 0.1μm per .1μm of thickness. • Excellent control on area of crystal grain growth.

13. Weaknesses of Al Electrode • Mostly columnar growth with very little surface grain size. • Bypassed U of A technology and focused the reaction area. • Will probably be more costly to perform due to size of reaction area. • Very vague on temperatures used, except in saying that it is below 500°C.

14. Pulse laser beam Dopant (n- or p-type) p-Si area with dopant a-Si:H a-Si:H Poly-Si growth through laser annealing. • May be possible to achieve grain sizes of 100μm or more. • Easy to dope for both n and p type. • Activates individual grain regions for polycrystalline growth.

15. Weaknesses • Pulse lasers are not cheap. They are costly to setup and require a lot of energy to maintain. • Narrow area for possible activation sites. • If not controlled properly, the laser will melt all the way through the sample and ruin the structure forming.

16. a-Si:H Mask Larger size p-Si p-Si substrate Heat p-Si substrate Poly-Si through a-Si:H melting • Uses heat as the trigger for polycrystalline growth. • Can choose where growth occurs through lithography. • Uses

17. Weaknesses

18. Technology Space for Si-based thin film solar cell Zhenhua Alvason Li ----------- Team 1

19. Distinguish of Si-based thin film technology • Abundant and nontoxic raw material • Low temperature process: • Lower energy consumption • Various low-cost substrates • Chemical Vapor Deposition: large-area deposition process. From http://tftlcd.khu.ac.kr/research/poly-Si/chapter4.html

20. Open Questions of Al Induced Crystallization (ALC) • N-type large grain Crystallization? • Potential efficiency of large-grained poly-Si thin film?

21. Open Questions of Al Induced Crystallization (ALC) • Tradeoff between energy consumption and productivity? • ALC requires 10+ hours growing and annealing • Making speed of poly-Si sheet is m2/minute

22. Beyond Silicon Solar Cells http://www.innolas.com/pub/images/Products/87.jpg http://www.innolas.com/pub/images/Products/59.jpg

23. CIGS Competitive Advantages • Highest efficiency of all thin film: up to 19.5% • Flexible: printing on glass, steel, polymers… • Non-hazardous chemicals • Self-healing: no degradation with 25 years warranty • High-speed and large-area printing method: It's like"Printing Your Own Money" After “http://www.aist.go.jp/aist_e/latest_research/2007/20070522/20070522.html”

24. CIGS Startups http://www.globalsolar.com/index.php?option=com_content&task=view&id=43&Itemid=95 http://www.globalsolar.com/index.php?option=com_content&task=view&id=38&Itemid=67

25. Why isn’t CIGS a Perfect Solution? • Right now, is manufacturing issues on a commercial scale • Long term, may face raw material supply constrains once achieve significant sales

26. Conclusions and Outlook • AIC can potentially reduce costs, but the productivity and performance need to be addressed. • Si-based and Si-free will co-exist for some time. • CIGS will have competitive advantages ----- as long as the raw materials are economically available.

27. AlternateTechnology Space Katrina Geren

28. Thin Film Resistors www.seed-solutions.com/.../N2PKVNA/SMT.htm Can be manufactured from many different materials Usually created by vacuum deposition (sputtering) Smaller grain size = higher resistance Resistance values dependent upon grain size, crystal orientation, and doping

29. Process Applied to Thin Film Resistors Advantages Larger grain size provides greater stability Disadvantages Large grain size creates lower resistance Probably restricted to lower resistance levels Lots of well established technology in the area

30. Memory Cells asymptotia.com/2007/08/20/brain-building/ Application of the property of Polysilicon that its resistivity changes with applied voltage Generally built from polysilicon diodes Inefficient

31. Process Applied to Memory Cells Advantages Theoretically large grains might improve performance Disadvantages No documented data on the use of large grain

32. MEMs Devices • Microelectromechanical devices • Integration of micro sized electical and mechanical devices • Used in many different products • Medical • MEMS Gyroscope • Electrical • Mechanical www.memx.com/image_gallery.htm

33. Process Applied to MEMs Advantages Large grain size would likely improve functionality Disadvantages Generally processed at high temperatures which seems incompatible with the crystallization technique

34. Thin Film Transistors • Basically a transistor created from layers of semiconductor, insulator, and metal contacts • Currently used in the driver system in LCD displays • Suitable driver for emerging display technology for emerging display technologies such as OLEDs www.personal.kent.edu/~mgu/LCD/tft.htm

35. Process Applied to Thin Film Transistors Advantages Low temperature More stable Lower noise characteristics Cheaper than alternative Disadvantages Temperature not as low as competitive technology Temperature not as low as required for transparent plastic substrates

36. Generalize Process for other Materials? Silver is a catalyst for GaAs, could polycrystalline GaAs be manufactured?

37. SWOT

38. References • Board of Trustees of the University of Arkansas, Application #: 11/728264. “Fabrication of large grain polycrystalline silicon film by nano aluminum-induced crystallization of amorphous silicon.” Filed Mar. 23, 2007. • The Regents of the University of California and Hitatchi, Ltd. Patent 6,635,932. “Thin film crystal growth by laser annealing.” Filed Aug. 6, 2002. Awarded Oct. 21, 2003. • Hitatchi, Ltd. Patent 7,238,582. “Semiconductor device and process of producing the same.” Filed Dec. 1, 2004. Awarded July 3, 2007. • Micron Technology, Inc. Patent 5,904,513. “Method of forming thin film transistors.” Filed July 1, 1996. Awarded May 18, 1999. • Astropower, Inc. Patent 5,496,416. “Columnar-grained polycrystalline solar cell and process of manufacture.” Filed Aug. 5, 1994. Awarded Mar. 5, 1996. • Mitsubishi Denki Kabushiki Kaisha. Patent 5,441,577. “Thin film solar cell and production method therefore.” Filed June 17, 1994. Awarded Aug. 15, 1995. • S.Gall et al. “Large-grained polycrystalline on glass for thin-film solar cells”, 21st European Photovoltaic Solar Energy Conference, 2006, Germany. • Personal interview with Li Cai on February 28, 2008. • H. Foll, http://www.tf.uni-kiel.de/matwis/amat/semi_en/kap_3/backbone/r3_2_2.html • Paul Maycock, 2007 Updated of PV Technology, Performance and Cost, Prometheus Institutes for Sustainable Development and PV Energy Systems. • Michael Kanellos, “Heliovolt raises more cash.” CNET News.com, oct. 21 2007. accessed February 2008. • http://www.globalsolar.com/ Company • Michael Kanellos, “Silicon vs. CIGS: With solar energy, the issue is material”, CNET News.com, Oct. 2, 2006. available. • Herner, Bandyopadhyay, Jahn, Kidwell, Petti, Walker. “Polysilicon Memory Switching: Electrothermal-Induced Order” IEEE Transactions on Electron Devices, Vol 53, No 9, September 2006. • K.N. Bhat, R.J. Daniel and E. Bhattacharya. “Stable passivation technique for high-temperature polycrystalline silicon on insulator MOSFETs for MEMS integration.” Electronics Letters Volume 42,  Issue 12,  8 June 2006 Page(s):721 – 722. • Domenico Palumbo, Silvia Masala, Paolo Tassini, Alfredo Rubino, and Dario della Sala. “Electrical Stress Degradation of Small-Grain Polysilicon Thin-Film Transistors.” IEEE Transactions on Electron Devices, Vol. 54, No. 3, Mar 2007. • Han et al. “Noise Sources in Polycrystalline Silicon Thin-Film Transistors.” Materials Research Society. Soc. Symp. Pro. Vol 744 2003. • Toutah et al. “ Correlation between the Aging and grain size of Polysilicon Thin-Film Transistors.” Solid State Phenomenon Vols. 80-81 2001 pp. 343-348.