Linde in Solar. - Linde Gas

Linde in Solar05Thin Film Si technology is growing rapidly.OEM AOEM BOEM CBulk Gas(N 2& H 2)OthersOthers3% SiH 414%16%SiH 4Dopants21%31% Bulk41%Gases(N 2,Ar,H 2)39%31%3%39%SiH 425%NF 3TCOPrecursorsNF 337%Nextgeneration precursorsRelative proportions of process gases for 3 different equipment setsIn order to reduce the cost per watt, Linde has moved from ‘traditionalsupplier’ to becoming an integral part of the photovolaic industry.Linde’s people understand the critical manufacturing processes andare developing innovative gas and chemical technologies to lowerthe overall cost per watt. These cost reduction technologies will haveincreasing impact as the industry moves to ever larger manufacturingscale.The critical process step in all thin film silicon technologies is depositionof doped silicon film from a silane precursor in a Plasma EnhancedChemical Vapor Deposition (PECVD) system. The result is a thin film ofsilicon on the glass. Typically hydrogen is also introduced to controlthe kinetics of the film growth. Dopants are incorporated throughprecursors such as trimethyl boron (TMB), diborane (B 2 H 6 ), phosphine(PH 3 ) and methane (CH 4 ).This process also results in silicon deposition on other surfaces in theprocess chamber such as the showerhead and chamber walls, whichmust be periodically cleaned. Typically a fluorine-based etch processusing NF 3 , SF 6 or F 2 is employed for this purpose.Nitrogen is a critical utility in thin film Si fabs and is used for multipletasks including purging vacuum pumps and dilution of toxic orflammable gases in chamber exhaust lines for safety.Another important step is the deposition of a transparent conductiveoxide (TCO) film on the front glass. This is typically tin oxide or zincoxide deposited via sputtering or using an organometallic precursorsuch as diethyl zinc (DEZ).Gas cost reductions are possible by a variety of methods, such as:On site generation of bulk gasesThe economics of large scale fabrication plants favour on sitegeneration of major bulk gases such as hydrogen and nitrogen. Thiseliminates the transportation and delivery cost of cylinders andenhances security of supply.Lowering Cleaning CostsMore than 50% of the capital cost and over 40% of the direct materialscost is consumed in the PECVD processes that deposit the active siliconlayers. The PECVD chambers require frequent cleaning of silicon residue.Replacing current methods (NF 3 or SF 6 ) by fluorine (F 2 ) can improvecleaning economics by up to 40%. Fluorine is generated on-site usingpackaged fluorine generators.Increasing ThroughputBy utilizing fluorine based cleaning the throughput of the PECVD processmay be increased by up to 6% at no extra cost. Additives in silane mayincrease deposition rates and thereby increase throughput.Improving cell efficiencyThe cell efficiency is strongly affected by the composition of the activep-i-n layers in the amorphous and microcrystalline steps. The cellefficiency may be improved by controlling critical impurities in theprecursor gases.Linde’s PV technology development roadmap targets each of theseareas, and many more. In every case, Linde’s approach involvesclose collaboration with key members of the technology value chain,including suppliers, PV equipment manufacturers and customers. Thisclose integration with the industry and alignment of research anddevelopment goals with the primary objective of reducing cost per watthave been critical factors in convincing more than half of all thin film Simanufacturers globally that Linde is the gas partner of choice for them.