Papers by Author: Adrien Danel

Abstract: Amorphous/crystalline silicon heterojunction solar cells are commonly made by low temperature deposition of front and back side thin films on bare H-passivated Si wafers, obtained by HF last processes. This work discusses the impact of HF last step parameters on cell performance, considering textured and cleaned Si (100) wafers. A complete native oxide removal is mandatory and achieved in a short time (< 5 min) by HF concentration higher than 1% (by weight). Above 1%, surface passivation and cells performance slightly increases with the concentration. The best process time is found to be the minimum time to deoxidize textured wafers, as seen by a good dewetting. For [H > 2% this is less than 1 min. Longer process times slightly degrade surface passivation. Post rinse and drying, provided they do not reoxydize the surface, were seen to have no impact. The delay between the HF last and deposition steps is critical and depends on the efficiency of the cleaning before the HF last. With a high performance cleaning, leading to a very good surface passivation (< 10 cm/s surface recombination velocity), 30 min delay has no impact and 90 min leads to about 5% relative degradation of cell performance. Regarding the HF cleanliness, HCl spiking is an efficient way to enhance robustness of surface passivation keeping < 10 cm/s values when the metallic contamination, including Cu, is in the sub 50 ppb range.

Abstract: After technical results presented the last two years and new results on volatile contamination, this paper reviews the contamination management in advanced microelectronic and proposes rules for advanced Integrated Circuits (IC) manufacturing. The competitiveness of a production line is insured only if right contamination management rules are applied. These rules must allow a fast introduction of disruptive technologies while keeping as low as possible associated costs: processing on shared equipments, determination of acceptable levels of contamination with a good understanding of their detrimental impact on devices, knowledge on contamination dissemination mechanisms. Moreover, a control of contamination using appropriate cleanings and metrologies is mandatory.

Abstract: Today, the use of Pods or FOUPs (Front Opening Universal Pod) in IC manufacturing leads to specific molecular contamination issues related to the enclosed environment made with porous polymers (mainly PEEK, PC and PP) that constitute these containers. Indeed, such materials are known to outgass airborne molecular contaminants (AMC), especially polymers additives [1,2]. They are also able to absorb volatile compounds present in their atmosphere coming from the connection to an equipment or from the release of wafers just processed [3,4]. As a result, a reversible outgassing of species previously trapped in plastic is possible. This is especially critical in presence of wafers sensitive to the released contaminants leading then to potential detrimental impacts. This cross-contamination scheme was clearly evidenced for volatile acids in presence of Cu layers leading to corrosion issues [4].

Abstract: The monitoring and optimization of wet clean and surface preparation processes is a major challenge in the microelectronics industry [1, 2]. Today, the main methods used in clean rooms are visual inspection by light scattering (principally applied to particle detection) and metallic contamination detection by Total-reflection X-Ray Fluorescence (TXRF). These methods, despite good sensitivity and recent progress [3, 4] are not sufficient, especially considering non-visual defects not measurable by light scattering, nor TXRF due to their chemical nature or to their size and location (TXRF is not applicable to light elements – with Z < 11 – and is typically a 1 cm resolution tool, with 1 to 2 cm edge exclusion). Non-vibrating Surface Potential Difference Imaging (SPDI), introduced in 2005 under the name of ChemetriQ® is an in-line, non-contact, non-destructive inspection technique based on the imaging of surface Work Function (WF) lateral non-uniformities [5]. Recent studies show very promising results for SPDI: high sensitivity to traces of metals on Si wafers with native oxide [6]; fast imaging capabilities of unpatterned or patterned wafers with sensitivity to chemical residues and charge [7, 8]. In this work, the ChemetriQ method is evaluated for in-line control of wet clean processes. The variation of SPDI data from various contaminants is compared to intra- and inter-wafer variations related to the cleaning and measurement conditions. Note that all wafer maps are presented with the notch oriented at 6:00.