CuInGaSe 2 films on 6-inch wide Mo coated polyimide web substrate in a roll-to-roll vapor deposition system from elemental sources is described. Material transport from the sources to the moving web substrate has been modeled by combining an evaporative effusion model and the gas flow kinetics and by experimentally determining the flux intensity profile. The model gives a reasonably good approximation of the Ga profile in the films. Poor adhesion of the selenide film to molybdenum has been resolved by depositing a thin layer of b-(Ga 0Á8 In 0Á2 ) 2 Se 3 precursor layer. Two-dimensional compositional mapping by energy dispersive spectroscopy of 5feet-long web gave 0Á88 AE 1Á9% and 0Á28 AE 2Á5% respectively for Cu/(Ga þ In) and Ga/(Ga þ In) ratios, indicating highly uniform film composition. This compositional uniformity translated to the uniformity in the devices fabricated on the web. The open-circuit voltages of the devices from the centerline of the 5-feet web were measured to be 0Á529 AE 0Á86%. A two-dimensional device efficiency survey gave 9Á2 AE 1%. The process was able to produce high-quality material, as defined by the best device efficiency, for a wide range of Cu/(Ga þ In) ratios. The best efficiency achieved so far was 12Á1% with MgF 2 anti-reflection coating.
A vapor transport process for continuous deposition of elemental and compound thin film materials is presented. The process saturates a carrier gas with a vapor from a subliming source. The saturated mixture is directed over a substrate at lower temperature, resulting in a supersaturation condition and subsequent film growth. The process geometry, comprising the dimensions of the saturation and deposition zones, carrier gas pressure and flow rate, and saturation zone temperature are determined by calculating worst-case characteristic times and simply insuring that the residence time of the carrier gas sufficiently exceeds these times. A model was used to design a system, which is currently being used to deposit 1–10μm thick CdTe films on a 10×10cm2 translating substrate. The process produces film thickness uniformity to within ±5% in the translation direction and across the deposition zone, with a material utilization of 50%. Linear translation speed of 12.5cm∕min has been demonstrated in depositing a 4.5μm CdTe film. The vapor transport process has also been used to deposit CdxZn1−xTe alloy films over a wide range of compositions by addition of ZnTe to the source. Photovoltaic conversion efficiencies of >13% for CdTe and >12% for CdxZn1−xTe have been achieved by devices fabricated from vapor transport deposited films deposited on to moving CdS coated substrates. Refinements are suggested for commercial-scale deposition.
Ag,Cu)(In,Ga)Se 2 (ACIGS) solar cells are optimized at bandgaps greater than 1.2 eV by varying composition profile of the absorber layer using a three-stage evaporation process. Numerical modeling and cumulative process data provides insight into the process. Silver alloying CIGS changes the optimized bandgap profile by reducing carrier concentration, and reducing bandgap gradients. The minimum bandgap position is controlled by the point when the film reaches I/III stoichiometry during the second stage of the three-stage process. We achieved a 19.9% efficient solar cell with V OC = 732 mV at a bandgap of 1.2 eV based on quantum efficiency.
To meet the stringent requirements of interconnect metallization for sub-32 nm technologies, an unprecedented level of flux and energy control of film forming species has become necessary to further advance ionized physical vapor deposition technology. Such technology development mandates improvements in methods to quantify the metal ion fraction, the gas∕metal ion ratio, and the associated ion energies in the total ion flux to the substrate. In this work, a novel method combining planar Langmuir probes, quartz crystal microbalance (QCM), and gridded energy analyzer (GEA) custom instrumentation is developed to estimate the plasma density and temperature as well as to measure the metal ion fraction and ion energy. The measurements were conducted in a Novellus Systems, Inc. Hollow Cathode Magnetron (HCM(TM)) physical vapor deposition source used for deposition of Cu seed layer for 65-130 nm technology nodes. The gridded energy analyzer was employed to measure ion flux and ion energy, which was compared to the collocated planar Langmuir probe data. The total ion-to-metal neutral ratio was determined by the QCM combined with GEA. The data collection technique and the corresponding analysis are discussed. The effect of concurrent resputtering during the deposition process on film thickness profile is also discussed.
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