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When formed by coevaporation, copper indium gallium diselenide (CIGS) films are typically more smooth than those formed by a two-step, precursor-selenization process. While some amount of roughness is desirable for minimizing reflection, extreme roughness or very sharp features can create a challenge in sputtering uniform, thin, transparent conductive oxide layers on top of the cell. NuvoSun, Inc. has determined that the surface roughness of the CIGS layer can be controlled by the initial temperature at which the CIGS precursor (PC) film is first exposed to a selenium flux during selenization. The resulting CIGS films are similar in roughness to coevaporated CIGS films, and the TCO layers on these smoother devices have fewer cracks and defects.

A new sputtered process for cadmium sulfide (CdS) has been developed that boosted efficiency of a PV device baseline (with single-stage, coevaporated CIGS) by ∼ 2.7% (absolute) to an average of ∼10%. The process is highly scalable to a roll-to-roll environment, with the maximum efficiency effect occurring at 0.1 mbar (∼75 mTorr) sputtering pressure. The efficiency improvement is thought to be due to two main factors: composition and defects. The CdS film deposited at high pressure (HP) contains more oxygen (primarily as CdO) than one deposited at typical pressures, with oxygen content higher towards the CdS-CIGS interface. The HP process produces an interface with less CdS-CIGS intermixing, which results in a junction with ∼ 5x fewer defects as measured by admittance spectroscopy. The performance improvement due to HP CdS occurs even with a very thin CdS layer (< 15 nm), thus greatly reducing the total amount of cadmium contained in the cells.

The thermal degradation and light capture performance of CuInGaSe 2 (CIGS) and c-Si photovoltaic devices were explored. Typically thin-film polycrystalline materials such as CIGS are hypothesized to be advantaged over single crystal Si solar cells as having lower thermal performance and improved light capture response. To this end, we present our evaluation of the thermal and light capture performance of three different CIGS devices, having different absorber layer stoichiometry and bandgap (E g ), and a c-Si device. Our results indicate that at the cell level these CIGS and c-Si photovoltaic devices have similar thermal degradation and light capture performance. The thermal performance of the c-Si and three CIGS materials explored were on average 0.40, 0.47, 0.51, and 0.48 % efficiency/°C, respectively. At low light levels (∼150 W/m2) the voltages generated by each device were within 90% of those generated at full light intensity (1000 W/m2). The current levels generated by each device trended linearly with the irradiance, and the Rs for each device increased with the irradiance although no intentional changes were made to the electrical contacts. These results indicate that both CIGS-based and c-Si devices will perform equally well in comparable real-world conditions. With regards to the performance relative to the CIGS bandgap, tuning the CIGS material stoichiometry, i.e. making it closer to CGS, should broaden the materials spectral response and provide beneficial improvements to the thermal degradation rate and the light capture performance of CIGS devices.

The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shell Solar Industries (SSI) were investigated. In our study, SSI minimodules were exposed to dry-heat 85°C, damp-heat 85°C/85% RH and aerobic and anaerobic room temperature and 85°C water baths. After 200 hours exposure to moisture-containing environments, the average device performance decreased by more than 30% that of the initial state. The observed degradation was primarily due to losses in short circuit current density (J sc ) and fill factor (FF). The as-received device layers were relatively dense and free of voids. Interestingly, unreacted Cu-Ga particulates were found at the Mo-CIGSS interface. Corresponding with these particulates, CIS-rich defects were found within the bulk CIGSS material. Post-environmental weathering, Kirkendall-like voids were found in the Al:ZnO and CdS layers of these devices. Additionally, ToF-SIMS analysis revealed the Cu-Ga/CIS defects were enriched in Na and O. Our results indicate that in addition to moisture-induced failure of the window layers, the unreacted Cu-Ga particulates and the corresponding CIS-defects may facilitate moisture and/or oxygen-induced failure of these devices.

Multilayer oxide thin film stacks of aluminum doped zinc oxide (AZO) and tin doped indium oxide (ITO) have been sequentially deposited on soda lime glass substrates by RF sputtering of AZO and ITO ceramic targets at a substrate temperature of 150 °C. The ratio of the AZO thickness to the ITO thickness is varied while keeping the total thickness of the stack constant. The electrical and optical properties of the multilayer stacks have been investigated as a function of this ratio and the number of interfaces. The experimental results are compared and their impact on device performance is demonstrated by simulations with validated AMPS-1D models. XRD and microscopy measurements have been carried out to understand the microstructure of the multilayer system and to establish its correlation with the opto- electric properties. The results have been evaluated for use of these multilayer TCO stacks as potential window layers for the photovoltaic solar cell applications.

In our study, Shell Solar Industries (SSI) minimodules were subjected to dry heat (85°C), damp heat (85°C/100% RH), and anaerobic/aerobic 85°C water baths. After 168 hrs exposure to moisture-containing environments, the SSI power generation decreased by over 50% of that of the original state. Analytical characterization performed before and after the exposure identified degradation of the Al:ZnO and Mo layers as likely device failure routes. To elucidate the observed degradation mechanism, individual Al:ZnO and Mo films were sputtered onto borosilicate glass and exposed to both 85°C/100% RH and a room temperature water bath. After 24 hrs the resistivity and optical transmission of the Al:ZnO films increased significantly following both exposure methods. XPS surface analysis of the films revealed changes in the O to Zn bonding ratio suggesting film hydration may have occurred. In addition, after 48 hours by both exposure methods the Mo films corroded, and the film resistivities increased. Our results show Al:ZnO layer degradation limits the lifetime of CIGSS based PV devices, whereas Mo degradation is considered a non-lifetime-limiting failure.

As device dimensions scale down, the back-end-of-line dimensions scale down as well, which results in an increasing resistance-capacitance delay of the interconnect. In order to compensate for the increase in the capacitance part, porous low-k dielectrics have been introduced in copper interconnect technology. Due to the highly interconnected pore structure of most porous low-k materials, liquid and/or gaseous species fill the pores of the matrix during integration steps. In addition, pores give rise to surface roughness at the top-interface and at the sidewall after etch, which makes it difficult to deposit a thin, continuous barrier in narrow trenches embedded in porous low-k dielectrics. All of the above makes pore sealing a prerequisite for reliable porous low-k integration (Guedj et al., 2004). Different pore sealing techniques are under investigation. In the case of low-k materials in which the porosity is created using a porogen, the porosity creation could also be shifted to a later phase of the integration scheme; either after low-k etch (Caluwaerts et al., 2003) or after metal CMP (Fayole et al., 2004; Jousseaume et al., 2005), which is referred to as post-etch-burn-out (PEBO) and post-CMP-burn-out (PCBO), respectively. It has been demonstrated previously, that the dielectric reliability could be improved considerably by these kinds of pore sealing techniques (Tokei et al., 2004). In this paper, both integration approaches are compared for porous SiLKtrade dielectric resin (k=2.2) from The Dow Chemical Company and the effect of both integration approaches on the interline capacitance, the dielectric reliability and electromigration are investigated and discussed in more detail

A positive-tone and aqueous-base-developable benzo- cyclobutene (BCB)-based dielectric material curable in air (CYCLOTENE * AD6000 series Advanced Electronics Res- ins) is described in this paper. The prepolymer is made from divinylsiloxane bisbenzocyclobutene (DVS-bisBCB) and BCB-acrylic acid. The formulation contains antioxidants that allow the prepolymer to cure in air and a diazonaph- thaquinone to make it photosensitive. Patterned films have high resolution, and via openings are scum-free without a descum operation. Whether cured in nitrogen or in air, the prepolymer produces a film with optical, electrical, thermal, and mechanical properties desirable for many microelectronic applications, such as packaging applications and as a planari- zation or insulation layer in display applications.